Useful when used correctly Rated 4 out of 5 stars
I only gave it 4 stars because it is situational. The main point is it can show just how little resources your add-ons probably are using. Even if you run a bunch they probably aren't slowing you down- they probably are speeding you up.
The key is to run it and then not obsess over the results- especially if you don't know how to interpret them. MAYBE it might point out add-ons with memory leaks. Also, add-ons that do more are going to require more resources while those that make minor changes or run silently in the background are going to tend to be dinky. That is how the cookie crumbles.
The bottom line is it is a handy tool if it isn't abused. I recommend installing it, running it periodically and then disabling it most of the time and not stressing over it.