One advantage is that you can publish HTML5 games to Xbox One and Windows Store using Visual Studio and UWP JS.
However, currently VS2019 doesn't support UWP JS, you need to use VS2017 for that. No word from Microsoft why...
An other advantage is the obvious, people can play the game in the browser without the need to download an executable or install anything on their PC.
Now it may not a good idea for a large project but me for example do like the idea of having maybe at least a demo version in HTML5 format that people can try and then download the full desktop version if they like it.
I also often see people share their games and asking for opinions and they share an executable or installer and I usually find my self don't bother downloading, installing the game but if it would run in the browser, maybe I would be interested to try. It is also an other thing to consider.
Regarding monetization, it is possible to implement in-app purchase and ads in to HTML5 games too, but AppGameKit and Tier1 currently does not support this.
If you host the game on your own website, you can implement adds around the game in to your website.
Regarding disadvantage, obviously it is meant to be used in the browser so when you package it in to a desktop or mobile app, it is not going to be as fast and there is also compatibility problems. HTML5 is best used in the browser, with AppGameKit, no point to use HTML5 for mobile and desktop but Browser and UWP.