Greetings, all!

I'm curious why there are so many multiclassing builds that go ClassOne for 12 levels, ClassTwo for 6 levels, and ClassThree for 2 levels (in any order). Has this been formulaically or empirically proven to be the best overall way to do things?

I understand dipping 2 levels in Paladin, Monk, or/and Rogue for quick and powerful benefits.