Sleeving is when you have the cylinder sleeves replaced with either new stock ones or aftermarket ones. I't's only required when you damage your sleeves beyond repair (by boring and honing).
Honing removes a lot less material and leaves a cross hatch design in the cylinders to help the reings seat.

I recently had my block sleeved (aftermarket) by golden eagle. When I got it back I took it down (along with my pistons) to my local machine shop and had them bore the sleeves (enlarge them close to the diameter you need) to about .002 pistons to wall clearance, then they honed it the rest of the way (to about .003 final piston to wall clearance)...

A bore and hone runs about $130 while a sleeving job runs about $749 for all 4 sleeves.