It's one of my most used utilities, as someone who can't help but nerd-snipe myself on the regular. Example questions that I've used it for, just in the last week:

If I work 42 hours/week, how many minutes is that per year?

I've downloaded 4.91GB in the last minute, what's that in Mbps? How long will it take to download a 76GB game?

This AWS feature costs $0.045/hour, how much is that per month?

This guy I read about traveled 58,000km in 27 years, what's his average speed in m/s?

How much would a 10cm sphere of gold be worth in GBP?

If a 36 inch pipeline can deliver 25580 acre-feet of water in a year, how fast is the water flowing in m/s?