This will be the second season opening my pool. I bought the house with the pool, so I didn't know how long it had been since the prior owners cleaned out the DE filter (i.e., take it apart and soak the internals in a cleaning solution for 24 hours and then reassemble), so I cleaned it out before the start of last season. When I did it, the filter was a mess. After I put everything back together, I opened the pool and had a great season. I ran my pump for about 8 hours a day and never had a single algae outbreak.
I was thinking of doing this again, but I'm not sure if it's something that needs to be done every season, or just once every couple of years. It's not that hard to do before you open, because the filter is already all disconnected.