Have you ever been asked to sub4sub?
I'm sure everyone has encountered people (and possibly done it yourselves) requesting to subscribe and in return they will subscribe back. This sounds like a great idea initially as you both gain a subscriber!
However this has a few major implications, first of all this is strictly against
YouTube Policy. "The number of users subscribed to your YouTube channel is a metric that reflects the number of people who are following your channel". Don't worry too much if you have previously done this a few times, but artificially gaining a large amount of subscribers can lead to channel termination.
Additionally to this, gaining subscribers is just a number and wont impact your channel. It could even possibly have a negative effect. Channels that have large amounts of subscribers with very low views can often be easily recognized, people see this as bad practice and then less likely to subscribe. So you may be forcing away legitimate viewers from subscribing!
YouTube closely guards it's algorithms when it comes to suggested, recommended, and subscriber feed information however some large youtubers have begun to crack the code through vigorous testing and experience. One such theory is the theory called "subscriber burn" which when broken down states that an inactive viewer will see less and less of you in their feed until the subscriber is "burned" or "burned out" This happens frequently with large creators and is one of the driving reasons creators need to promote themselves on various platforms to reactivate "burned" subscribers.
Supported by
MattPatt from Game theory
There is a similar theory based on just as much evidence that when you release a video your response rate (or the number/percent of people who interact with your content) within the first 24 hours can set your video up for success or failure in the long run. The target response is floating above 35% viewership to subscriber ratio. This gets harder and harder to achieve when you've inflated your subscriber count using methods like sub4sub.
-Various sources throughout the years.
For these reasons any form of sub4sub/like4like is not allowed on the Freedom! Forums or within the network. If you do see anyone requesting sub4sub, please report the user and they will be warned by someone form the moderating team. Remember to still be respectful of the user, we don't want to to initiate any arguments over this and they might just not know any better.
Thanks to @Anthony Smith for the additional information!