In terms of YouTube TV, this is only useful for browsing live channels and launching one. Once you launch it, you are in the YouTubeTV app as normal. It would take extra steps to exit back out to the live TV interface to change channels. I guess it would be worth it if, for example, you wanted to consider all your options through Amazon Channels, such as live Showtime channels (if you subscribe), or if you have something like Philo or wish to browse whatever is on Pluto TV (though I think you only see a limited selection of Pluto channels).
Unlike YouTube TV, you can't customize the order of your channels; they remain in alphabetical order even in your favorites list. You also can't customize the order of the services in the live grid guide (as far as I can tell). Fortunately for me it defaulted in the following order: YTTV, Showtime, Pluto.
The biggest benefit for me is the additional voice commands for YouTube TV, namely tuning to a specific channel, which I couldn't do before via Alexa.