I'm service manager for an enterprise desktop environment. All our machines run Windows and we don't support anything else.
Why do I use Linux at home? Many reasons from setting up my own servers for fun to getting a break from work, but more so because it forces me to always be learning and be curious. Curiosty and continued learning are, in my opinion, essential to being successful in IT.
Depending on the job role Linux may be required, but just learning Linux will help you regardless.
In regards to seeing it on a resume or credentialed, it would tell me the candidate is willing to try new things. Which is always good.