What is with dogs and emptying their anal sacs?

So, I’ve had dogs before and never experienced this strange thing. My new doggie scoots his tush on the floor about once every two to three weeks or so. I read that this means his anal glads need to be emptied. Instead of paying to have the vet do it or the groomer do it, I just do it myself…no biggie. I’m just wondering, is there a diet that would make this a less frequent need for him? Or is there a reason why his need to be emptied so often as opposed to why other dogs never or rarely need to have this done? Advice? Comments?