What does enhance do for troops?

Enhance will upgrade the troops to a mid level above their current level.

T6 troops enhance to T6+, T7 troops to T7+. etc.

The enhanced troops will have higher stats than the base troops for attack defences etc. But they are not as good as the next tier up.

E.g. T7 Gladiators have an attack of 46 - T7+ Gladiators have an attack of 50.

You can check the troops stats in the Command Center Building.