In terms of specifics, PowerShell's strengths over C# for scripting are particularly in PowerShell's the ability to succinctly navigate hierarchies (folders, but also other folder-like trees) in a way reminiscent of shells from time immemorial, as well as to easily interleave native binary calls (and pipes/redirects/captures).
Some of it is the difference between grabbing C# binding for libgit off NuGet, LINQing my way through a the git DAG for the information I need versus running `git show xyz` or `git describe` directly in a shell and capturing that into a variable or piping that to whatever my next steps are. Depending on my level of abstraction and how often that script is called and if I'm paid to write that script or it is getting in the way of what I'm actually trying to work on, I use a different tool for the job.