The program is offered as is, there might be serious bugs.
I would call it an alpha version, but I use it myself, so test it, comment it, but be careful when you use it with real data.
Which folders are written
Files (default called ".buvt-filter") can be placed in the Source-tree to make it possible to skip certain files and folders.
They work somewhat similar as ".rsync-filter" do for rsync (as a matter of fact I considered using the same file (and syntax) as rsync, but I had to give up on that because I can't figure out how rsync works)