I don't like point-buy for potentials because it forces you to make decisions about the end point for your character, when you are creating your character and potentially don't have a great sense of how everything fits together, rather than allowing you to develop in an open-ended fashion. Eliminating potentials entirely is better.
On the other hand, you are choosing a profession, which is far more critical in deciding the end point for your character (unless the game allows profession switches). Choosing potentials at start is in the same spirit - the end point is pre-ordained in a way.
I'm not saying having point-buy for potentials is better or worse, just that it is not unreasonable.
I tend to go for a mix of both : your potential starts as the average depending on your temp stat (I use the averages from RMSS), and then you have 20 points to allocate to increase those potentials, with two restrictions:
- you cannot go above 100
- going from 99 to 100 costs 5 points instead of 1.
Since I also use standard spread for initial stats (90, 2x80, 2x70, 2x60, 2x50, 40), it makes choices easier but still significant. The only potential problem is that it cannot cope with extreme character concepts (for instance, a stereotypical 'brawn without brains', with very high physical stats and low mental stats). But I tend to dislike that kind of extreme anyway, so it's not too bitter a pill to swallow :p