Action Points? Encumbrance? What?

[PvK]

It's not that "you get 3 Enc for free", it's that every unit has a base Enc value, which is the cost in fatigue of attacking. Base Enc does not reduce AP's, and Enc from equipment or age or whatever is added to that to get the total fatigue costs for actions. Most but not all humans have base Enc 3. Non humans may have more or less or zero base Enc. And if you have zero base Enc, you don't incur fatigue by attacking but you do from spellcasting (and equipment encumbrance is added for spellcasting - hence the thread someone created warning about putting marble armor on spellcasters).

Oh, and another thing to factor in is that some use of AP's carry over to the next turn. The typical way this shows up is while someone can always attack once per turn, they can't move as far on a turn after they have attacked.