I myself have even gotten into situations in World of Darkness or other Crystal Tower raids where I'm starting to run dry on TP and have to CONSCIOUSLY hold off on popping skills to allow my TP to regen to an "acceptable amount." (This is assuming you don't have a rogue in the party who can use Goad on you, or someone who can pop the other TP regen skill that the name of which escapes my memory).

The second situation....is even easier to get yourself into than over-spending.....and that is DYING and being Rezzed. When you are rezzed, your health, MP, and TP, are all at faaaaaaar less than 100%. So, you're rezzed in combat, and even though a healer can quickly get you back to 100% HP, that doesn't apply to TP...in which case...being able to quickly pop a skill like Invigorate right after a taunt can prove to be a saving grace to some degree, as you don't have to worry about getting to critical levels of TP.