Let's say you are organizing a sports event. In a knockout tournament it is really advantageous if you could only face weaker teams, until the final game where you face a team which had to fight all the other strong teams instead.
Two months prior to the event you number each initial spot in the bracket, and you assign a number to each team - sort them alphabetically or something, it doesn't really matter. You tell everyone that assignment will be done by shuffling using a well-known PRNG, and you'll take the beacon value one month from the event as seed.
The T minus 1 month point is reached, you download the beacon value, feed it into the PRNG, and shuffle the teams to get the final bracket. The algorithm and all inputs except the randomness was fixed in advance, so you cannot manipulate that. You have committed to the seed without knowing it, so you could not have possibly manipulated the seed either.
Everyone can verify this, so everyone will agree that the drawing was done fairly.
Two months prior to the event you number each initial spot in the bracket, and you assign a number to each team - sort them alphabetically or something, it doesn't really matter. You tell everyone that assignment will be done by shuffling using a well-known PRNG, and you'll take the beacon value one month from the event as seed.
The T minus 1 month point is reached, you download the beacon value, feed it into the PRNG, and shuffle the teams to get the final bracket. The algorithm and all inputs except the randomness was fixed in advance, so you cannot manipulate that. You have committed to the seed without knowing it, so you could not have possibly manipulated the seed either.
Everyone can verify this, so everyone will agree that the drawing was done fairly.