The main bonus is that Linux doesn't suffer from all the instability and security issues that Windows seems to be renowned for.
Windows hasn't had stability issues since Windows 98, 15 years ago. A lot of Mach3 users still use Windows 2000.

I use Mach3 because I like Windows. All my other software is written for windows, and since Mach3 runs in Windows, I don't see a need to jump to a different OS.

Mach3 isn't perfect, but I doubt that LinuxCNC is either.

I really hope to have a control with S-curve accel for my next router. If Mach4 doesn't have it in the next year, then I may jump to the K-Flop with their KMotion control software, although I'd probably create a custom front end for it.