Just a few benefits of VMs I can think of here:
.....
* Historically, VMs were sometimes emulated and thus slower than operating
a system "bare-metal". On my systems, installations in VMs are often
faster than installations on the machine directly because they can make
use of caching (e.g. for installation media which need not be provided as
physical media but can be image files as well), libvirt has its own DHCP
to provide IP addresses quickly etc. such that systems inside it respond
faster to certain installation tasks like getting an IP address over DHCP.
We should mention the various virtualization hardware assists built-into Intel and AMD CPUs
which allow VMs to run with near-native performance. Not to mention the assistive code in
the linux kernel itself eg. TLB, etc. These technologies were available beginning in the early
1960s (Atlas) and especially after 1965 (OS/360) and again after 1970 (MVS and VM/370) in
the IBM mainframe universe.
HTH
Linux-Fan