If you trim the branches so there are a few leaf nodes, then you can use them to start new plants. They root readily in moist soil, though a bit of rooting hormone won't hurt. I have used completely dried leaves in Phantasticus and Ebenaui tanks. If I was really lucky and managed to get a few leaves to cling to the trimmed branch, the geckos would hang in there most of the time - perfect camouflage.
As for pruning, I don't think there are any rules, just make it fit your enclosure.