If it's a crack, part of the work of leading is keeping the gear and the rope out of the way of the jams and out of the way for putting your foot in the crack. Putting the gear all on one side is a big advantage along those lines.
The only time I can think putting gear on opposite sides is safer is when you want to trap the rope where a fall involves some penduluming. For example, say your gear is 4 feet off to the left from where you're going to pull an overhang, with a 4 foot sling on it, then if you can get a piece 3 feet off to the right (at the same height) with a 4 footer on it, then the one on the right will keep you from swinging more than a foot to the left (instead of 4 feet). (Of course, keeping yourself from getting tangled up in those slings is a major challenge....)