Rounds take a fight further away from what a real NHB fight is whether on the street or in a cage. Since they don't add legitimacy and actually take away from it (think of fighters who have been saved by the end of a round and then won) obviously they exist for entertainment value. They ensure that there will be a standup at least every five minutes and The UFC knows its fans prefer standup fighting. It also gives fighters a chance to rest so that people can see fighters operate at a high-level of intensity for more time. Rounds take away from a submission expert's chance to lock in a submission hold but again The UFC encourages stand up fighting. Rounds exist strictly for entertainment value at the expense of realism.