It helps cut down on backwashing, which is maintainence which takes time and money (for DE at least). Its is certainly not a requirement to use them. And, if you gets lots of pollen and fluff like we do, it can actually reduce the volume of water going through the skimmers once the socks are clogged up. Personal choice.

As for rotating, I do it because it is quicker for me. Take a whiff of one of those things coming out of your pool and then tell me you want to put it back in without some type of cleanup. Sunlight is a great disinfectant.