I have been doing this for years. I find it helpful when going to refactor a part of the app that has problems. I then go look in the code and see TODO comments I added a while ago. Then I am 100% sure I really should fix that up. Yes they can get stale but usually they tend to be helpful.

I really like reading todos written by other devs to see where a feature was left incomplete. It's so much easier to see it right in the code rather than lost in a ticketing system.