VMWare Player is a very useful free application. If you have one computer but need multiple operating systems it can save a lot of time. While VMWare is not the most efficient way it is very efficient at what is does. The only way to get more efficient would be to run everything in the native OS, or hardware. Sometimes rebooting multiple times a day can be a real headache. It is slow and time consuming when the application that is needed is in a different OS.
The downfall of a Virtual Machine is that running another Operating System inside of your native Operating system requires more system resources. To properly run a Operating Systems in a Virtual Machine requires also system requirement for the Virtual Machine are plus those of the Operating System being run in the Virtual Machine. Even more is required to run the Virtual Machine as the Native Operating System and all applications running in the Virtual Machine Operating System must be included. As all of these requirement stack quite quickly a system must be very powerful to run a Virtual Machine. Unlike old systems new 64bit systems have the able to scale much easier and therefor can run Virtual Machines easier.
VMWare eliminates many reboots during the day that could cost hours of waiting. Running or testing Buggy software can cause a system crash, but crashing a Virtual Machine doesn't cause the down time that a full system crash could cause. There are many good reasons to use a Virtual Machine. VMWare is definitely leading the pack.
Testing Software is one great reason but, what about when your need to run say a Linux app while working in some windows tools at the same time. Turns out that is not a problem. Start VMWare and run your app just like normal. Another reason is gaming. While dual-booting is an option sometimes you don't want to have to wait between cycles. If the system can handle it then dual-booting can be avoided. Windows a Linux can be like oil and water and some changes can make your dual-booting systems well no longer boot one or both. The Virtual Machine avoids this since neither system touches setting of the other.
Tryout a Virtual Machine and you can see the benefits. Don't own a Mac and need to run some Mac software no problem start your Virtual Machine and the problem is solved. There are so many reasons to use a Virtual Machine and with computers as power now there is really no reason not to use one.