As others have said, you need a power point reserve above 0 to maintain psionic focus, which is needed for several feats (and may some Soulknife abilities, not sure...). Anyway, there are creatures, spells, powers, abilities, traps, etc. that drain power points. So the more you have, the less chance you have for being reduced to 0 PP and the less chance you have to lose the ability to be Psionically Focused...
Oh, and IIRC, the class does not give you 1 Power Point. It gives you the Wild Talent feat for free, which gives you 2PP. And the purpose of the Wild Talent feat is to make you a "psionic character" so that you can take other Psionic feats.