There is more leverage on the wheel bearings, spindle, king/knuckle bearings, differential, etc. But this leverage also helps with articulation as increased wheel travel at the benifit of a decrease in suspension travel.

But I've not seen anyone wasting bearings/parts due to spacers, but then again I've never seen anyone running 3" spacers !!

I've got 1.5" all around. I Like 'em

You could just run some 2" offset rims and have the same effect also....