Security is one advantage. If you're running a server with multiple containers and you're concerned about attackers taking over one of those then you can isolate them more from each other and the rest of the system using VMs.
(Addendum: I'm not that experienced when it comes to container tech and I heard you can isolate your containers pretty well these days. Virtualization has also changed over time and isn't as "isolated" as it was once; for example virtualized guests are often executed directly on the host's CPU. I'd definitely look into this more before deciding on one approach.)
(Addendum: I'm not that experienced when it comes to container tech and I heard you can isolate your containers pretty well these days. Virtualization has also changed over time and isn't as "isolated" as it was once; for example virtualized guests are often executed directly on the host's CPU. I'd definitely look into this more before deciding on one approach.)