as [MENTION=6678119]Jackinthegreen[/MENTION] has stated, any Psionic class chooses their power effects off the pool of Power Points.
Psion gets the most Power Points.
The trick to being a Good Psion is being a good economist of your PP. If you're someone who is handy at keeping track of numbers and determining if this particular action is worth this amount of investment, considering the risk of possible future investments needed... then groovy, a Psion might be your kind of caster. You've got tons of control over just how much Oomph you put behind everything you do.
if the thought of that gives you hives and convulsions, then a Psion might not be for you.
It's great power, requiring great numerical responsibility.