A beginners bracket is a separate group in a different tournament, that only allows or only attracts non-top tier teams. This can be accomplished by having the beginner bracket not having a trophy for the winners, no prize, or having entry requiring approval from a tournament coordinator. The basic purpose is to allow these second-tier teams to have a fair chance to complete, play against players at or around their own skill level as well as increase the competitiveness of the top tier bracket.
From a simple mathematical perspective this is desirable because its easier to do a simple round robin. Because adding another team adds n-1 games (where n is the number of teams) to complete a simple round robin splitting the teams in half requires less games. Even if it is not a round robin this removes some of the matchup inequality because the teams are not selecting from such a wide range of team skills. Having left a zone tournament last week it would have been easy to split the 13 teams into two brackets one of 6 and one of 7. This would have also allowed every team to play every other team in their bracket.
By not offering a prize or trophy for the beginner bracket you allow teams, which would not have a chance to win the trophy anyway, to have a better tournament experience. While the teams on the top tier still get to keep every ounce of their bragging rights. Whether this would happen entirely naturally or would require some kind of rules to prevent some team from owning the beginner bracket for lols, is a matter we will have to leave for the future.
So this methodology would allow for the teams to have more fun, a more competitive experience, where they have less chance of getting badly beaten, and have more good games. Downsides? I really don't know any.Oh, TagDaPlanet