With elimination type brackets, if the number of teams you have in the event is not a power of two (i.e. 2, 4, 8, 16, 32, 64, 128) you will need to have byes in the first round in order for your bracket to play out correctly. If you do not have the byes in the first round of the event then you will end up with byes later on in the event which is not ideal. A tournament that does not start with a power of two number of teams, is to setup to get to a power of two number of teams in the second round. That is done by setting the appropriate number of byes in the first round.

All standard brackets are done this way.