What is VMOptimizer? Well, being able to run other operating systems without having to restart your Mac is undeniably useful, but over time performance can degrade which can be frustrating if you're trying to run a game. You might have been able to improve this performance by running a defragmenter such as iDefrag, but that only solves part of the problem.
Most files only suffer from one kind of file fragmentation, but virtual disks suffer from three different kinds of fragmentation which means the performance degradation caused by it is multiplied. Now it is possible to tackle each kind of fragmentation individually, but that's awkward and time consuming. Things get even more complicated when you add the fact that virtual disks are usually split into many files and they might be using snapshots.
This is where VMOptimizer steps in. It quickly and efficiently tackles all three kinds of fragmentation in one go.
VMOptimizer is also able to make other optimizations that can significantly boost performance, such as realigning partitions that happen to be misaligned.