Every OSR RPG takes a slightly different approach to how they handle classes, from using the traditional four, to adding more classes, to stripping away classes. Personally, I like a nice happy medium of using a different four classes. For example, in my current Kickstarter, it includes four new classes for LotFP: the Conspirator, Corpse Worker, Prize Fighter, and Witchdoctor. This is because it was originally meant to be an entire rules hack of LotFP, replacing all of the core classes. In the end, I decided to just make it a supplement however. But making setting specific classes allows for the players to have characters that fit well in the world without being flooded with choices, in my opinion.
Inspired by: http://osrsimulacrum.blogspot.com/2017/11/classes-dismissed.html