I've shot dozens of images of my full-sized colorchecker chart with a Canon 5D2. Different lenses, different frame-fill, different focus, different exposure, different light.
Processed these with Adobe DNG Profile editor. The resulting profiles show very little differences, so little to be insignificant. Just try it yourself. Shoot the target at at different frame-fills and different focus, make several profiles and see if you can tell a difference.
So, within reason, I don't think it makes much difference. Of course, if you shoot the target with a ultra wide angle lens that suffers significant vignetting and distortion, and you grossly over or under expose, and you use some wierd uneven light, then the garbage in, garbage out rule may apply.
For me, the main benefit from making custom profiles is in using different base tone curves.