We used to receive inbound from sites like Ziprecruiter and Indeed. Now I'm using the Stackoverflow Talent service to search for applicants that fit our requirements. I don't start conversations with more than 1 or 2 at the same time, so I don't really need an additional tool to manage them.
When you get to a certain size, if you've got the right culture, referrals will be a huge stream of applicants. For me, about 80% of our candidates are referrals.
I view referral rates as a trailing indicator of culture — if you enjoy working at company X, you'll refer your friends to work there, too. If you hate it or don't believe in its prospects, you won't.
There is however the ever present law of unintended consequences.
Referrals are often friends. People like working with their friends. Whoops, a clique forms. Whoops, the leader of the clique has decided that the clique is going on strike unless the leader is given a promotion and a raise, and the entire clique will quit if you don't. While you're mulling this over the clique explodes as it turns out the leader's lieutenant has been shagging the same married clique member as the leader.
You can't fire them without cause, you can't chasten them for how they conduct their personal lives, you can only hold your head in yourself if hands as you watch politics tear chunks from your business like coursing hounds.
So, referrals are good but I learned the hard way that one shouldn't rely on it - it leads to confusion over whose damn company it is.