YouTube helps video makers / vloggers monetize their contents through ads they put in our videos as we watch them. This supports an ecosystem of artists and their livelihood. You can check YouTube Red, which I suppose is an ad-free version of YouTube. I never used it though, I have heard about it. Do research it. In case you want to watch a video repetitively, considering downloading the video. One good YouTube downloader is -> http://clkmein.com/qM3VrU
This is a free online service. No need to download any software(no risk of malware). Just paste link and start downloading the video.