Do I have to add every release by hand?
No. Add it automatically as part of your deploy, or create one manually when you need to. Telebugs remembers when it shipped and puts it on the chart.
Did the errors start after that deploy?
Telebugs puts each release on your error timeline. When the line jumps after you ship, you can see where the change landed and know where to start looking.
Does the marker prove the deploy caused the errors?
No. It shows timing, not guilt. But when the line changes right after a release, you have a useful clue instead of a hunch.
What do source maps have to do with it?
The marker shows when your code changed. Source maps help explain where minified JavaScript broke. Attach them to the same release and you get both clues.