There aren't a whole lot of uses for this (I think virtualization sucks in general), but the main use for a typical end user is to run legacy software but still upgrade their system as a whole.
This is particularly important given that Lion won't include Rosetta. Using virtualization, you could upgrade your system to Lion, but run Snow Leopard in a virtual machine, in which you run the legacy software.
It's also handy, of course, to run a virtual windows system on your Mac, and to run software that requires keys that expire (backdate the virtual machine).
Software, such as TuneUp, is tied to a particular machine. I don't know if the software enforces that, but if it did, I suppose you could run it in a virtual machine, and then you can move that virtual machine around as you upgrade your Mac. ("lifetime" license but tied to a particular machine is stupid.)
This is particularly important given that Lion won't include Rosetta. Using virtualization, you could upgrade your system to Lion, but run Snow Leopard in a virtual machine, in which you run the legacy software.
It's also handy, of course, to run a virtual windows system on your Mac, and to run software that requires keys that expire (backdate the virtual machine).
Software, such as TuneUp, is tied to a particular machine. I don't know if the software enforces that, but if it did, I suppose you could run it in a virtual machine, and then you can move that virtual machine around as you upgrade your Mac. ("lifetime" license but tied to a particular machine is stupid.)