His issue sounds kind of unique. I've never heard of a casino adding to your bonus playthrough via your winnings.
I do use bonuses because there is no downside to them...specially when they are paid out piecemeal. Even if you don't complete the playthrough for the full amount, you will get a part of the total bonus depending on how much of the playthrough you finish. The part you do get, you can then withdraw or use as desired. I'm not sure why you wouldn't use a bonus tbh.