I always disable it. Having everything using the same exact colour palette is boring/homogenized. The themed icons are even worse, simultaneously killing iconography art and making it much more difficult to differentiate between apps in the app drawer quickly.
Apparently not according to the other comments here, but I absolutely love Material You now that a lot of apps support it. Not having every app have its own color scheme just feels comfortable and IMHO makes a lot of sense together with the system-wide dark mode.
Also, the app drawer always has unthemed icons, the themed ones are only for the home screen where I like to keep the few apps that I use often, so not having a colorful mess for a home screen is a bigger plus for me than losing the ability to recognize them at a glance, because I know exactly where on the home screen they are anyway.