The character is great at fighting in situations where others cannot:
He can fight without penalty to AC or attack in a space up to half as large as the normal allowed (2.5ft for a medium creature).
He can occupy the same square as a creature two size catagories larger than himself (normal is 3). Doing this does not deny the creature his dex bonus to AC.
He gains a +2 dodge bonus to AC against melee and touch attacks when prone and fighting defensively.