I can't tell how many rounds were lost just because people thought it would be more efficient to save their ults rather than using it to secure round wins. It's so frustrating watching people save their ults the entire game when that's not how ult management works. On average you'd get 1-2 charges on your ult every round unless it's an absolute stomp. So saving ults is just not really efficient unless you are trying to combo ult with someone else.

I mainly see this problem with Sage and now Viper players (huge influx of vipers with the buffs) as their ults don't really have a set time that you should use it almost always such as a phoenix ult to use for entry or Jett ult when you are on Eco, etc.

If you are a sage and you are in a 4v2 situation, you might want to consider using your ult and potentially getting 2 charges afterwards from the 2 people trying to retake the site. You also save the gun your teammate died with so it helps your econ anyways.

If you are a viper, maybe consider using your ult to secure the round or at least make it super hard for the enemy to retake. Believe it or not, pushing into the new Viper is absurdly hard, you're basically 1 hittable after 2 seconds of being inside.

The game is won on the round wins not who wins the round without needing to use ult. I rather you "waste" your ult than not use it at all.

TLDR: Use your ult, they're helpful in securing round wins and round wins = game wins.