For me, I prefer trem cover off. I don't like having to mess about with screws, especially when there aren't any metal inserts for them to thread into and it's just wood. Here's the back of my Strat and my Sterling. Easy access to add or remove springs, or adjust trem claw as necessary. Sometimes I change the tuning on the Sterling, and need to mess about, and it's just much easier and faster with a lack of cover.