Dealing with leaking first stage/o-ring problem? Adjusting tank band? Passing gear through a narrow spot where both rig and human can't pass at same time (wreck/cave)?
Yes, yes and read Shadow Divers!
FWIW I haven't used a weight belt since OW; just one of the benefits of diving BPW. I don't like cold water and am lucky enough to be able to avoid anything below 19C, so I can dive up to a 5mm suit with hooded vest - which is enough to keep me warm for ~45 minutes at 19C - and only need an SS BP and a few pounds in non-ditchable trim pockets on a cam band (with a single steel tank)