I consistently hear people on YouTube complain that the subscribe button doesn’t do anything for viewers, now that channel notifications are controlled by the bell. But it does do something: it puts the videos from that channel in your subscription feed, which is readily accessible on all versions of YouTube. So why do people act like it doesn’t exist? I think it’s super convenient, especially if you’re subscribed to a ton of channels and don’t want your notifications feed flooded with new videos.
Over time that subscriber section has become less prominent. At one time it was the way to find content you wanted to see. I think most people now just use the feed YouTube gives you.
Subscribing does seem to affect the algorithm. If nothing else it should help the creator pay the bills so you can keep getting videos from them.