Not necessary, but potentially useful depending on your profession.
I keep my network relatively tight: people I have worked with, or done work for, or friends I have in related professions.
I’ve got a couple of connections that are not work related, just for a bit of breadth, but they are very much the minority. Nothing looks sadder than your mum vouching for your skills. 😀
(I’ve had a few interesting job offers through it – as well as a loads of professional recruiters – but I’m not actively job hunting at the moment, so it’s more just a reminder to my boss that I could be 🙂 )