Forgetting to add -g (or -ggdb or similar) to CFLAGS/CXXFLAGS when enabling FEATURES=splitdebug seems to be an at least somewhat common mistake, and you don't get any obvious indication of what is wrong if you try to use the resulting .debug files with gdb. (It just says "no debugging symbols found", which is true, but didn't help me solve the problem.) Plus once you do figure it out you have to recompile anything you want debug symbols for. It would be nice to provide a warning to the user if they forget this so they don't get useless .debug files.
