Doubles can be good because they're heavy compared with single hooks. Stickbaits originally designed to be used with trebles often require pretty large singles (used instead of the trebles). If you don't want to use giant singles, then plugging doubles could be the answer. I don't really like doubles though. Not sure they're much safer than trebles (safer for me) and I think they could be pretty bad for hooked fish. Double hooks on the tail could be bad for fish - catching them in the throat, etc.