It entirely depends on how far anything is from the camera. If your panorama only consists of far mountains, the horizon, and everything sufficiently far away that 3–6" of parallax shift won't matter, well, then it won't matter.
However, if there is something in the foreground, such as light poles, sail masts, trees, fenceposts, then their parallax shift will have a noticeable difference. Either you work around them by making sure they are not in your stitch overlap region, or you spend a lot of time in post to smooth them out, make them look good, etc.
BTW, an L-bracket won't solve your panorama-on-a-ballhead problems. The L-bracket only lets you mount the camera in portrait orientation, which is more desirable to get a taller panorama. In order to eliminate parallax shift, you have to have the ability to locate the camera precisely forward/aft along the optical axis. For most camera+lens setups, this requires the ability to shift the camera backwards (towards the photographer) from the ballhead mount. So for the easiest panoramas, you need both an L-bracket and a fore-aft slider bracket.
For panoramas, I find the ballhead to be the least desirable tool. It is only useful to create a level base, on top of which all of the panning and panorama action happens. A panning base below the ballhead is not useful; only a panning base on top of the level position is useful. On top of the panning base I use a fore-aft slider, with the lens mounted in portrait mode with my permanently mounted L-bracket.
If you're concerned about bulk of the L-bracket, then you need to consciously decide: would you rather make compromises in just about everything but the panning base when making your panorama, or would you rather get the best panorama you can get? There's really no way around that decision.
It is entirely possible to get good results. Although I do own a panoramic head, not only does it weigh over a kilo, it takes a huge amount of space and so most panoramas that I capture for myself are done using a ballhead.
The first feature that makes it easier is using a ballhead with an independent pan-lock. That way you can lock the ballhead to a certain tilt and rotate around 360° to get a strip with a consistent horizon.
You have to make sure that the base of the ballhead is level which using a tripod alone is tedious because legs are not easy to adjust precisely. To get around that, I have leveling-base inserted between the tripod and head. It adds a little bit of height and weight, if you choose a lighter one.
Capturing image using a ballhead that is level and rotated with a fixed tilt for each band can produce very good panoramas. The issue that it does not solve is parallax which is due to the fact that you are not rotating around the exact nodal point. The closer elements are to your lens, the more parallax issue there will be. For panoramas taken at a distance such as landscape vista or city skyline from a vantage point, results can be fantastic. There will be problem stitching indoor scenes, particularly in rooms with lots of objects at different depths, like columns and chairs in a church for example.
It is hard to measure how many issues because stitching software is very complex and sometimes has issues even stitching a perfectly taken panorama but knowing when parallax occurs will let you choose view-points that are less prone to the issue.
Depends on the panorama you're shooting, and the subject distances. Far subject distances (landscapes), etc. with sufficient sunlight for the right shutter speeds, you can even get away with handholding for shooting grids (multiple rows) to stitch together.
But indoors, or small interiors, then parallax becomes an issue, since the ballhead only lets you rotate around the tripod hole, not so much the no-parallax point in the lens.
For 360/spherical panos, a ballhead can make it difficult to grab zenith/nadir shots for full coverage.
And with single-row panoramas, there may be issues of not maintaining a level pitch or roll as you rotate in yaw, which can create curved horizons and not-straight panos when it's all stitched together. You can typically correct this within stitching software, but to get a rectangular pano as an end result, you may have to crop more than you want to.
And if you're using a telephoto lens with a very small angle of coverage, it may be difficult to precisely place overlap and ensure complete coverage with no missing spots, vs. using a panohead that's marked off with detents for precise coverage.
If you're shooting panoramas, the first thing you need to be concerned about is that the base of the head is level, or at least parallel to the plane of rotation of the camera. Level the base, level the camera, and with a short-enough (28-35 mm prime for a "full frame" body) lens and parallax issues will be minimized, unless some of the subject area is very close to the camera.
You can get away with this some times, but you'll be better off getting a focusing rail (or at minimum a long Arca-Swiss style rail, mounted along the lens axis) to let you adjust to the nodal point of your lens.
If the base of the tripod head is parallel to whatever you want to pan across, you'll only be rotating in one axis relative to your subject. If you use the ball head to control the alignment to your subject, you'll be introducing a second degree of motion when you rotate the head, and won't necessarily be getting a clean capture.
Ideally, I'd use a Gigapan head on a leveling tripod for panos (up to full 180x360); if weight's an issue (or there's an unusual situation) I'll use a RRS pano rig and move it manually. One nice thing about the RRS pano kit is that it also serves as a gimbal for a long lens. But if I need to work without a net, I'll use a short focal length lens and level the tripod before leveling the camera on the ball head.
If you use Arca-Swiss clamps you can achieve a measure of parallax correction by, as I said above, using a long A-S rail aligned with the lens axis. If you need to use a long lens, and it has a tripod mounting ring, this can also help you deal with parallax. But the time to test where the nodal point for your lens is before you need to know it. That way you can choose the best lens for the gear you have available. And you can't have too much overlap! It makes it much easier to stitch a pano if you don't need the corners of a wide angle lens.
I work with the guy (Jim Walker) who shot this tour of the National Air & Space Museum and this reflects both his experience and mine doing other panoramas, including with some very jury-rigged arrangements.
A small lightweight solution for single-row panoramas:
- A leveling base, so that you have a reference plane. The alternative is spending a long time adjusting the legs of your tripod. In practice outside of panoramas the levelling head can also replace a ball head.
- Something that rotates along a single axis. This can be a plain "3D" head (often sold for video) or a gimbal head with the relevant axis locked, but you can also use a very simple one-axis head.
- A L-bracket to shoot in portrait mode if necessary