found religion

So I usually play on emperor alone or on emperor with 1-2 friends. And I must be doing something wrong or maybe something changed after the last patch I don't know (I didn't play for the last 2 months or so). The thing is that founding a religion takes away so MUCH damn production early game...

So let's say you take over the home of a religion. Do you now get the benefits of that religion? Should you continue to spread that religion or replace it with your religion? I find the documentation lacking so if there are better sources please let me know.