4PCs-in-1 clones your first Windows system with a drag and drop giving you two Windows systems. Now you are the master of Windows rather than Windows being your master. You can choose to run whichever Windows system you want with a double click. Then clone again until you have 4 Windows systems all on the same partition, all in the same drive, all on the same drive letter. No partitioning is reuqired.
Turn Windows into a disposable Operating System. If it crashes what do you care? Switch to the next one. Freeze your mission critical system (adding no more software to it) without freezing your entire computer. Give your most important application its very own Windows system. Put your applications into a 4 bedroomed house instead of squeezing them all into a one bedroomed studio flat.