What is the purpose of Pokemon tiers?

Question

It feels stupid to ask this, but what are the Pokemon tiers' purpose?

Comments

Not a full answer, but https://www.smogon.com/forums/threads/tiering-faq.3644714/

Answer 1

The main reason is to allow people to use the Pokemon they like, while also not being severely handicapped for doing so. It also gives variety, so people can play other tiers when they get bored of OU.