It's not really a matter of keeping the folder 'clean' The files are actually stored in a type of database. OE needs to keep track of every record in that database. When a record is removed from that database, a 'hole' is left in it's place. It doesn't take long for this database to become very inneficient. OE's database is rather delicate and has a long history of becoming corrupt. If OE tells you to comapact, I highly recommend that you let it and that you don't do anything while the compaction process is running.