There are two good reasons to find a new job before you quit:
(1) it improves your chance of landing that new job, and
(2) it increases financial stability.
When backpacking in the woods, all good campers know the rule “Leave the campsite better than you found it.” It’s a good rule for life and work, too. Deciding to make things better at work before you leave does a lot of good. It helps your colleagues, who have to pick up the pieces, succeed.