What happens if you watch your own YouTube videos?

Newcomers think it will increase channel view time, but it does not. Self-viewing does not count for monetization requirements.
So, self-viewing can increase public visible views on the video and helps to increase a little view time not much.

In all, not much benefit of viewing, rather you waste your time knowing you already own the content.

It will be counted as a new view if you watch your own video for the first time. However, this does not imply that YouTube would count a new View each time you watch your video.It will no longer be counted as a fresh view on YouTube.

As a result, repeatedly watching your own video will not help you boost your View Count or Watch Time.
Furthermore, if you pay attention to the Analytic part of your video, you will find a measure under "Unique Viewers."