Deb I use the hinge method and tape them back up...I use clear packing tape from the dollar store and just do the sides. I don't tape it up tight, just enough so it won't blow open. The cover does act as a little greenhouse.
You could cut them off completely since there are a lot of seeds that will come up naturally and they aren't covered but the cover helps keep the critters out and they won't get drowned by a heavy rain. Another good thing about the cover is if they do sprout before your last frost they stay safe and warm

especially if you are doing annuals.