I don't know why having a wheel size of 16 is better than say 15...but maybe someone knows that one. I can't think of any advantages.
About the wheel fitting, it depends on what year they came off of. Grand Cherokees from '93-'98 (ZJ) will fit as they have the same bolt pattern as YJ's (5 on 4.5"). From '99 on they changed bolt patterns. So if they're from a ZJ, you're good.
- SOA 2.5" OME Springs, 8.8, 4.88's, 35in ProComp MT's on 15x10 ProComp StreetLock Wheels