I use them and switch them out every 2 or 3 days. The way I look at it is if I dont use them the junk will end up just settling in my sump and become a nutrient source. For me its much easier to deal with socks than to regularly clean out my sump.
If they will fit, go with big socks. I have 7 inch diameter socks and get a week + out of them before I have to change them.
ever since i started using one, i had a lot of my algae problems go away. that was probably a coincidence but it keeps my sump/skimmer from getting really dirty with brownish stuff. like others said i much rather clean the sock every other day then remove the whole sump.