When does “thanks for getting that done” become excessive? It becomes excessive (and diminishing) when it’s said every time a task is accomplished, regardless how trivial.
What does “thanks” really communicate, when it’s said every time? It says:
* “If I had the time, I’d have done it myself”;
* I wish I had the time so I *could* have done it myself?”
* You cannot be trusted to accomplish anything worthwhile, so when you do something well, I must ‘reinforce’ that with a ‘thanks'”.
So supervisor, stop saying thanks, and bestow trust. It’s been earned.