I think that when collaborating both parties need to understand that results aren't a given.
I've had channels ranged from my current 7 Subscribers, all the way up to what was my largest channel at 3,000 Subscribers, for me personally, I like extending a helping hand, but I prefer it to be an "ongoing relationship" not a one-and-done scenario.
What I would typically do is if someone approached me about working together to help them grow, I would ask a series of questions to them to see how much they wanted to "grow" what was there plan after they grew, etc.
From my experiences, once there growth has been achieved it can go one of two ways... They either continue growing or they take the help from "you" and then don't apply what they have learned.
I'm not saying either approach is "wrong" but I like to see/hear about others successes, and I like to build friendships.
My last collaboration was when I was apart of the Fullscreen Network, was invited onto a Weekly Podcast for an extended period as the other 3 channels grew.
All was well until each channel got to about 1,000 Subscribers, then I was unfortunately let go from the podcast. Was I used? Maybe. Am I mad about it? Not really.
As I said before, when helping a "smaller" channel as a larger channel, you have to take into consideration that some folks just want to gain a higher sub count and aren't looking for friendship or working together in the future, it's just the nature of the beast.
I personally look forward to growing myself, and helping others grow as I go on, so for what it's worth, I'm always willing to work with like-minded people and build business relations with others!
TL;DR
It's not bad to collaborate, just be careful of who you do it with!
-DieHard