Heat is a show in Smackdown Vs Raw 2007. Being shown on Monday on the calender, it has no PPVs or championships, as it is a minor show. The show can be used to train jobbers and have squash matches to keep morale up. The show can feature any superstar on the Raw roster, and shares Raws commentary team and General Managers, as it is the Raw preshow. It has a Smackdown counterpart, called Velocity.
Heat can be used to train jobbers, meaning you can train new talent to put them on the main roster. The three matches can also bring in extra money for your brand.
Eventually, most jobbers on Raw will need to be used on Raw and not Heat, meaning that eventually Heat would run out of talent. Also, having only three matches will cause some jobbers to have to wait for a while to get a match.