So I've come to understand that subscription exchange is bad practice. So I'm wondering how far this extends? I have some friends who have their own channel and they have recently subscribed to mine. Is it safe for me to subscribe back? How many reciprocal subs constitute infringement of the rules? Personally I feel bad if someone subscribes to my channel only for me to ignore theirs. It's a little like the follow back on twitter. So my question is just this - can I subscribe to my friends channels to support them, or do I risk losing my channel?!