Running a virtual server allows you to run a server application on its own virtual machine, this eliminates the chance that (when running multiple applications from a server) the underlaying requirement for each apllication conflict.
In comparison to docker the full server can offer more native capabilities for some applications, while other applications simply only run on a full OS.
So by virtualizing the servers one large piece of Hardware can be used to run multiple servers and you can (sometimes dynamically) allocate resources as needed.
The backups can consume all computing power put of office hours while the other applications share during Office hours as needed.. sometimes a bit more for VM A and sometimes a bit more for VM B.
Off course monitoring overallocation is a thing as you might end up with bottlenecks caused by peak loads that occur at the same time.. the issue would be bigger when running on dedicated hardware.
And off course having multiple hardware platforms interconnected allows for a VM to be moved from hardware platform to hardware platform without interruption (license required) meaning you can perform hardware maintenance without an outage.