I used to be real concerned about getting knots in my leader. I've stopped worrying about it because I started thinking about the knot that connects my tippet to the leader. It doesn't prevent me from catching fish. I don't get a lot of knots anymore. But, if I do get a knot, I don't spend a lot of time trying to undo it. If I can't undo it in about 15 seconds, I just cinch it down and get back to fishing.
Birds Nests are a different story. I'll spend about 2 to 3 minutes on it. If I can clean it up, great. If not, I just cut it out and tie on a new leader and tippet.