What do you use virtual machines for?

I was wondering what everyone uses virtual machines for these days. I have recently began to use them in order to learn ubuntu and read a lot about how people have multiple in order to run other services. Care to elaborate on what your uses for them are?

I use it for quite a few things but some of the basics are -

rather shady software at times, accessing websites that I don't really trust a whole lot, and I have some programs that only work on a legacy environment.

I never considered using it for shady sites, so to speak. I wonder if that would help when torrenting to prevent possible viruses and such?

It can help yes but of course only to certain extents

Quickly testing different operating systems, or running different operating systems for certain software that doesn't like the OS I run.

Being able to run pfsense and freenas on the same machineĀ