Stats affect how certain talents are calculated. For example, if you have Spell Proof talent and Strength, Agility, Power all at 250, that will give you +10% resist all. If same stats are only in the 220-230 range you will only get in the 8-9% range. Different talents use different combinations of stats to calculate the bonuses given. If you look up the talents on central you can see the calculations for most.
For the universal defenses, Spell Proof breaks down as 2x Str, plus 2 x agility, plus power, devided by 125 Spell Defy is 2x Str, plus 2 x agility, plus power, devided by 250
My suggestion, look up the skill you 'd like to improve, like PP in this case, see the equation, and you'll know the important stats to improve
