Around the course, there are a couple of danger areas when it comes to lazy sheets. The first is immediately after the start, especially if you were luffing on the line. Another is around the leeward mark, when the now-lazy sheet may have been all the way extended if you just came up from a wing. If you can take the slack out in these situations, then do it; if you don’t have the opportunity, just be aware that on the first tack off the line or up the new beat you may have excess sheet to trim in. On some level, always be cognizant of your sheets so that you can avoid snares or a sloppy tack.