All of the racks I've built so far are meant to be used with lids on. Now the pros are that you never have to worry about an escapee and humidity is very easy to keep up. The negatives are cleaning isn't as fast and feeding can be interesting. On feeding day some of my little ones get so excited the minute I lift the lid off I have a little worm in my face ready for a meal. Overall though knowing I will not lose a snake because of a rack failure is such a positive for me I don't mind the minor negatives.