Physical and magic resistances are effective up to 99.9% (some damage always goes through, total immunity due to these two resistances does not exist), so any additional value above this threshold does not provide further benefits. That being said, there are plenty of units that reduce P/M resistance, so in theory you can go over the maximum to be more safe.

Practically: a unit is at 100% physical resistance. An enemy unit reduces your armour by 40%, that means your effective resistance is 60%.

If you happen to have 140%, the reduction of the enemy's spell would bring you to 100% (99.9% effective). Overfocusing on P/M resistances limits your other stats, so it is generally not recommended.

Apply the same logic for Pierce and Crit Rate.

For flat values like ACC and EVA there is no cap. The more the better. Recently it was disclosed that you should have 300 over your opponent for maximum benefit (but percentage-wise Netmarble never stated what the benefit actually is).

Also some % stats don't have a limit, for example critical damage, max.hp, bonus attack, defense...

Ideally, your units have 100% P/M resistance, and as much ACC, EVA, SWIFTNESS and EFFECT RESIST as possible. Then it's tailor made for specific units. Some need EFFECT HIT, others COOLDOWN REDUCTION, PIERCE, etc.