As I recall I needed my tool exactly 3 times in about 3 years: first time, it was a broken spoke on organized century ride. I did not attempt to fix or true the wheel, but the tool helped me to remove brake pads, so I can get to the closest food/service stop. LBS there has a rear wheel loaner, I did not need to to fix the wheel there. The second time my bottle holder got loose, and the last time, the chain broke. Using my chain tool I made it shorter and it allowed me to finish my ride. And I have had couple of the flats, that needed tire lever.
I agree that the tool is heavy, but I'd rather have couple hundred gramms on the bike, than quit my ride. Nothing was life and death situations, but the tool helped to finish what I started. However, I remove my saddle bag for races.