Mostly keep.
But every few years I have a purge. The last one was about 3 years ago. I sold about 100 through apps like webuybooks and ziffit and made about £100. I gave away four or five times that number to charity shops and some were just thrown away. I still have several hundred at least.
If I like a book I struggle to throw it away and some I read over and over.
I do borrow books from the library too so I can try out new things without it costing anything.
I would hate to live in a house without many books. The only rooms in my house without books are the bathrooms and the utility room. Oh and the hall and landing. Used to have a bookcase on the landing but managed to do away with it after the last purge.
Editing to say I don't do kindle. I like the feel and the smell of real books too much.