Linux fits most of my needs, is very lightweight compared to windows, uses less battery, and has the added benefit of being free & open source. (I won't even mention the career-related benefits) Say what you want about whatever company but I will always trust something that's free & open source to something that's closed source.
It's not about demonizing everything else or seeking validation for "nerd cred", like some people will inevitably say. It fits my needs, so I use it when I can. If I need something windows-exclusive, then so be it, I use windows that day. The joys of dual booting!