First of all, congrats on having a 40 year homebrew setting! That is damm impressive. Now on to the question at hand.

I think it only matters as to what kind of story you want to tell. Also the amount of time you have to dedicate to a world building matters. Some game masters just don't have the time to fully flesh out a world which is why they use prepackaged settings like Forgotten Realms or Star Wars. It gives a good basis for what the players can understand and can relate to as well as a variety of different tropes that you can use for your game.

Personally I beg, borrow and steal the parts that I need and only make the parts that don't already exist. I played in games where both the players and GM did world building. It does give the players more agency and they feel that what they do matters in the grand scheme off things.