Next time you want to write a few lines of C# to verify a detail about syntax, count how many clicks you need to go through to create a new console app project / solution.
It's much faster to just hit the + in LINQPad.
It's quite useful when I'm reviewing someone else's code, or if I'm "in the zone" in a large change. I can verify some syntax in a few seconds, as opposed to the minutes it takes to make a throwaway console app project / solution.
It is kind of like csharprepl[0] but more powerful for the scenarios it targets. However, since it only supports Windows it's a non-starter personally so I never used it much.
https://github.com/oleg-shilo/cs-script