After spending half an hour on the following post it occurred to me that a houseplant forum search for "nicking" might yield more accurate information. Sure enough, I found several threads containing Al's explanations, but I spent so much time on mine that I refuse to delete it!!!!!
Here are a few of the threads. The nicking discussions aren't long but I think Al's post on the first link explains the effects of nicking vs pruning. Use the search box at the top of the page to find even more threads.
http://forums2.gardenweb.com/discussions/1458989/fiddle-leaf-fig-question?n=1
http://forums2.gardenweb.com/discussions/1465570/pruning-ficus-lyrata-to-branch?n=24
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My now-superfluous post:
Ah, I see; most people seem to call that nicking, not slitting. The reason you haven't found info on it is that few people do it, but Al has gone into it the few times he's been asked. I'll describe it as best I can from what I remember of his posts about it.
Anyway, you would use a sharp sterilized (just in case) knife to cut a small horizontal wedge through the cambium (basically the living usually green layer under the bark) right above a leaf node. Nicking (or pruning) above a node stops the inhibitory hormone from the top of the tree from reaching it, letting it respond to hormones that direct it to grow. The same thing happens when you prune. Whether you prune or nick, the amount of back-budding you'll get depends on the plant's condition.
IMO, if the stress that caused your ficus to drop leaves still exists, nicking or pruning won't have much (if any) effect so long as the plant is still under the stress that made it drop so many leaves. I'd guess that's because the weakened plant isn't producing the hormones that would stimulate growth above ground.
That's been my experience. My ficuses didn't respond at all to tip-pinching last fall when they were still weak, but now after months of proper care and increased spring sunlight they're growing like crazy, including a lot of back-budding far back on its once-bare branches, without any intervention at all from me.
I think that's an accurate description of what I've read!
Q