I put a form of this answer here, but I can add a bit here as well. As much as I hate to say it, this is a giant "it depends" answer. If your current SQL Server box is a beefy 128GB memory, 4x12 core proc box that is constantly running at 80% utilization it's probably not going to be the greatest candidate for virtualization. However if you have departmental SQL Server databases/instances that are sitting on 4GB machines running a dual-core processor and 99% idle, I'd say that's a good candidate for consolidation and/or virtualization.

Notice I threw consolidation on there? That's definitely another option if you want to still make use of some of your hardware without needing to virtualize. Also there's licensing concerns. If you consolidate you pay for one OS license as opposed to new one for each VM you spin up. There's lots of variables at play, just need to find what works best for you.