How do you guys know when it’s time to downsize your collection and what to sell

I hope this is ok to be asked here not looking to directly sell anything here but wondering when do you guys realize it’s time to sell off stuff? I have a bunch of Omnibuses that are non modern era and I’m not a fan of that era but bought them before I realized I didn’t like the non modern era and I have almost 180 Omni’s and it seems to be too many thanks for any replies