We don't trim hostas. In the Autumn they just turn brown and I pull off the leaves and pitch 'em. I suppose you can trim whatever you would trim with a plug-in trimmer with a cordless, just not for as long.
We have arborvitae and yews and other shrubs. I know a cordless just doesn't have the 'oomph' for prolonged trimming/pruning, so I long for a gas-powered one.
I do have/use an 18v Black&Decker blower that has string trimmer, edger, hedge clippers that use the same battery/charger system. It does OK, but doesn't have much stamina for big jobs.
Jim Ricks