Running multiple operating systems within a main operating system is a productive way to get work done. You can improve security in some cases and make it much easier to go through multiple scenarios versus dual booting. The security scenario is one where you run web browsers in such an isolated way that the spread of malware is greatly diminished. The idea is less convenient in practice however, but there are some cases where the inconvenience is worth it. Another secure scenario is where certain technical tools for building programs can weaken a system so running them in an isolated environment can improve things. Best of all, isolated compartments are easier to backup and put back into action. The downside is that some visual tools do not present quite as well in virtual environments and that can be a place where they fail.