There are tens of hardware platforms (although, some people would say that there is only one - computer ;-) ). Each one has its own advantages over others and disadvantages as well. For example Intel is the most used platform for desktops, ARM and MIPS are widely used in embedded systems and so on. Sometimes, a need may arise to test/debug executable code written for platform other then the one you have access to. For example, what if you have to run ARM code while using Intel based desktop?