Subscribing to a Youtube channel is not about opening up yourself to getting bombarded with emails about the channel having new content. Sure, you can get those emails, but you can turn that off. Your Youtube home page will show the latest videos from the channels you subscribe to. However, that should be a good thing if you like the content from those creators.
Before I go into why subscribing is so important, let us discuss the points about views, ads, and the "thumbs up/down" aspects of Youtube.
When a video on Youtube has views, it helps the channel admin/creators to know how well received the video was. It is a tool that helps a channel focus on that style of video production, or figure out what made it work. Or it tells the creator that they need to stop working on those types of videos, and find a new focus all together.
Thumbs up/down is the same thing, sort of. It is useful, but we also know that there are a LOT of trolls on the internet. Also, there is potential for a rival channel to play a little dirty. It happens. Again, welcome to the internet. However, those are a minority. The thumbs give viewers a method to give feedback to not just other viewers, but also to the creator.
As for the ads. If you do not use an adblock system, or you have it turned off on certain websites like Youtube, that is greatly appreciated. Ads are a great way to build revenue on Youtube without having the viewer do anything except watch the video. Sure, there is other funding options...Kickstarter, Patreon, or even Youtube's own "Fund Me' button. However, ads do not require any serious commitment from the viewer/fan.
All of that means nothing to sponsors. That is the issue behind why subscribing is so important to content creators. Like I said about crowdfunding sites, and ads...serious content creators are looking for methods to generate revenue. This is either to help fund their channel, or to help make what they love their actual career. Regardless, potential sponsors look at a channel's subscription numbers. That number represent the amount of exposure that channel has, and the potential for that sponsors product/information/brand/etc to get out there to the masses and get recognized. Basically speaking, sponsors are where the money is at.
Youtube creators aren't trying to harass you to be a subscriber to the channel just because they want to be mean, or to win some sort of glorified internet popularity contest. WE do that because we are trying to build our brand so that we can create more, and better, content.
So, please subscribe when you get a chance over at the Notes and Nerds channel on Youtube!