It prevents people that want in on the Odin/Behemoth battles from doing so and it prevents people from entering a zone to complete a quest objective.
That's the whole point. Other people are only inconvenienced for a short time, it's better than everoyne being inconvenienced because of every areas having channels/instances.

Capping the participants in those fates is the only way for them to be fates without it being a clusterbomb of lag and server crashing.