I find them invaluable when programming, before the program is complete enough to have a formal issue tracker. There are always a lot of pending obligations and incomplete ideas that I have to record so I don't forget them. I also like the rhythm of completing stuff and deleting them from the list. The list is just a text file that I keep in source control along with the code, so I can retrieve old versions if I have to. Thus I don't worry about deleting items once they are completed or stop being relevant.

For real-life stuff the usual wisdom applies. Plenty of stuff on the list never gets done and that is fine. It's just a place to park pending stuff.

I use an org file these days but a plain text file was fine before I switched to org. An app would be ridiculous, in my opinion.