Quick: How many grams are in an ounce? How many euros is $1 worth? What's the square root of 65? Windows 10's search in the taskbar can answer these and similar questions.
It's similar to performing quick calculations in your browser's address bar, except you can do this on your desktop -- no need to open a new tab or your calculator for instant answers.
Some calculations and conversions don't require you to enter the equal (=) sign before giving you the answer, which is pulled quickly from Bing search (so you'll need to have web search enabled and an internet connection).
Alas, when I typed in "meaning of life = " it did not return 42, but it's still pretty handy.
Tip: Use Start Menu Search as Calculator in Windows 10 [Into Windows]