In my latest game project, I've decided to use TP as a third vital meter.
You know the deal: If your HP depletes to zero, you're done, MP, no more magic/skills/whatever.
But TP is by default a safe thing. Not in my game. If TP goes to zero in my game, it's almost worse than a Knockdown (death status), because that character gets hit with a nasty status ailment that weakens their every ability, and is difficult to recover from. Also, every action that requires movement (attacking/casting magic/etcetera), will deplete TP, or in my game, it's EP, Endurance Points. If you don't have enough Endurance, you may as well wait, or defend. Also, some equipment will make actions cost more Endurance, some less. The idea is that you want to end battles quickly, but not so quickly that fatigue sets in before the next battle. I've always thought this was a good mechanic to have, but maybe not everyone thinks so.
I appreciate all constructive thoughts on this. Let us discuss with full hearts and open minds.