If you get shafted by your employer during maternity and they pull coverage early, and give you misinformation re: COBRA timing, and it's not an open enrollment window with the state exchange, even if you can convince the state exchange to let you in before the next open enrollment period, the soonest they might do that is at the end of the month.

And if you have any ongoing treatment issues, the temporary/indemnity insurance you'll have to buy won't cover any preexisting conditions.

TL;DR–if you get left in a lurch, you're still stuck on temporary insurance which won't cover preexisting conditions.