The maximum dexterity bonus is a cap on the bonus to armor class (AC) from a character's dexterity modifier. This cap applies only to AC; it does not affect the attack bonus for ranged weapons, the attack bonus from weapon finesse, reflex saves, nor dexterity-based skills (most of which are subject to the armor check penalty instead). It is, however, reflected on the character sheet, which will show the capped modifier if the maximum dexterity bonus applies (and the capped modifier will be in red if it is lower than the character's base dexterity's modifier).