Install the watchOS 6 beta to Make watchOS 6 Better
If you are actually going to use the watchOS 6 beta as it's intended, that's the perfect reason to install this beta. You can report to Apple how the features are working, bugs that pop up and offer feedback on the new features and changes.
Apple can then use this feedback to make the Apple Watch better, which means we may not have the need for a fast watchOS 6.0.1 update this fall to fix a major problem that flew under the radar. It also means less waiting for fixes in future updates.
This is really only applicable to developers in the program officially, who can use the Apple Bug Reporter and developer forums to share feedback.