I'm Assuming that you have default roster sizes (check under League Settings > Rules, Roster Rules):
Active Roster Size: 25
Secondary Roster Size: 40
So let's say you've just completed your 1934 season and now you've advanced to the game to offseason (so the game date is somewhere around early/mid-October), I would think that if you dropped the Secondary Roster to, say, 30 then and then advanced the game by one day, all teams would cut players in order to get down to 30 players.
If you currently have Active & Secondary Rosters Sizes at something other than 25/40, it shouldn't matter. It just really depends upon how many players you want available for a free agent draft.
Important: Before you do this with your save, either make a backup, or create a new game just to test it out. Good luck!