It's fun to shoot different guns. I see no advantage to sticking to one type. However, I do want to either keep it simple for a carry or home defense gun, or make sure I am very, very familiar with operating any gun chosen for that purpose. It would suck to forget to disengage the safety.
Disadvantages to sticking to one type of gun (at least for me):
-boredom (means I won't want to shoot at all)
-remain unfamiliar with other weapons that may be better than what I have
-unfamiliar with other weapons that I may find in my hand one day for one reason or another.
The more the better.