By running MemTest, you can ensure that your computer's RAM is correctly functioning. This is a good thing to check whenever you buy a new computer, install new ram, or change the configuration of your machine (for instance, to overclock it). If you are the sort of user who likes to push the performance of your machine to the edge, relying upon whether your machine will boot after your new BIOS tweaks is a poor way to determine the safety of your new settings. Use MemTest as a true test of stability.