How do you find media to watch?

I've seen many people have insane setups to download things automatically and NAS' with tens of terabytes of capacity, which i don't understand at all.

I have a 1 tb drive from 2013 of which I'm using ~850GB and most of the space is used by series i have already watched and haven't bothered to delete.

What are you storing to need so much space and how are you finding so much good content that you actually want to save?