Skimmer socks are before the filter, the slime bag is after. So you would think that the slime bag is not going to help - its not helping to keep the filter clean.
Well, I think differently, based on a grand total of observing one person - me.
I used to have to clean and recharge my DE filter once a season due to pressure rise (about after 2 months). I would also get a fine 'dust' on my pool floor occasionally. I would have said dead algae except for the fact that my FC stays steady, my CC are zero, and I pass an OCLT. I gave up trying to figure out what it is. However, I would have to vacuum multiple times before I could get rid of it. Then I started using a slime bag whenever it appeared. It took care of it with one cleaning. Then I noticed that my filter pressures started staying low all season.
My theory is that whatever is in my pool is really fine, and after a while it does finally get stopped by my DE filter, but it really plugs it up. The slime bag (which is a much finer filter than a skimmer sock) grabs that stuff before it can build up in my filter.
That is my theory for now.