A comment is more powerful than a like, a dislike or a follow. It expresses the argument behind liking or disliking. It is more accurate to explain some thoughts. It is more applicable because of the video. A video is more expressive and therefore it deserves a loud expression of lookout.
There are thousands of people who watch the videos. If you can get to know the thinking of all those; imagine how many directions of thinking can be achieved. This is a general advantage. If we focus on the commercial privilege; the companies can have valuable feedback in the form of comments. If they buy YouTube comments, they can know how rightly the advert has explained the features of the product, in case of a commercial.
If it is for a social cause; then it is easy to understand how many people are supporting the idea, for what purpose and in what way. When somebody writes it is easy to get the attitude psychologically.
There is a great variety in the outlook of the people since everybody thinks different. A video is more influential and pressurizes people to react. With YouTube comments you can receive many.
The more number and the varied quality give you an opportunity to improve. It is with the comments which are both positive and negative. Positive comments increases your confidence and negative makes you understand the shortcomings. Remember, the customer is always right? You can take a note of this golden rule and make improvements.