The tree does not need to spend energy to keep leaves, they are it's energy source. Before leaves drop, in normal situations, the tree will have pulled nutrients out of the leaves before they fall. There are not many reasons to leaf prune, one is to allow more light to hit the figs, another is to reduce the water needs of a cutting or transplant. I would think you are not going to help the tree much by removing any, the tree will drop them on it's own time. It might help with rust but I don't have much of that and don't do anything but rake leaves once at the end of the year, maybe someone else does it. Figs can bleed for some time if the cut is made with a very sharp tool rather than one that does a little crushing as well, so look out for that, that is not good.