Well, that's like saying should I put sauce on them or not. You'll find a WIDE variety of cooks who do and do not do it.
A mop is a good technique to keep the food from drying out and puting a little flavor.
A baste is usually a little thicker/richer and trying to add taste not just moisture.
I always suggest, put three racks in. One, nothing extra. 2nd one, baste it with a flavorful baste 3rd one, mop it.
Hope it helps a little. You'll have to experience it to see if it helps you.
Smokin'