It's not the worst idea....especially near the glass where algae forms between the sand and glass. It's also good to do to get waste that hasn't been sucked into your filter back on top so you can siphon it out yourself. If you have African Cichlids - especially Mbunas - you won't have to worry about it much, because they constantly move the sand around and dig in it. I can't say I ever had fish die from the anaerobic gases that are released, but many say it's important to keep it stirred up to prevent those "pockets."