I was with a network on my old channel, it might have been the fact they were a crap network, but it made no difference to my channel at all. I believe at the end of the day whether you are with a network or not, it doesn't change the amount of work you need to put in to your channel to help it grow. Back then, I didn't think like this, I believed that joining the network would help me grow without me putting more work in(like an idiot). All I got from the network was access to copyright free music which you can get anywhere. The forum wasn't anywhere near as good as this one, I got NO support when I asked for it. This time, if I do eventually join a network I am going to spend a lot of time researching and not rush into any decision.
So to sum up, I don't really think you need to join a network as with a bit of searching around you can get all the same benefits some networks do offer you, without actually joining one. But I expect people who are in good networks may disagree with me. I look forward to hearinf their opinions about it