Accessibility, for me, is the cornerstone of a good app experience. Let’s leave beside the typical arguments surrounding making your app useable for the largest population of users, and the fact that it may just be legally required in a few years to have an accessible app.
I think the biggest argument for having an accessible app is so that power users can use blazing fast. And typically that means everything being keyboard first on desktop and swipe/touch first on mobile.
How does your app respond when someone uses an obvious keyboard shortcut like (cmd + a) on a table? How does it respond when someone double clicks? Or swipes?
I think the better you pay attention to accessibility standards like Aria and HTML best practices, the more likely your app is to perform correctly in certain situations.
I also think there are several Javascript components that lend themselves to building poor interfaces. For example, apps typically have sidebar nav or tab based navigation. These can hide things from the core view of the app. In my opinion, it’s best for the user if these type of components are all routed.
This gives each of them a url which can be shared by your support team to help get a user to the right place. Or, the deep link can be used by the user to help someone on their internal team get to the same view.
There are several different things that tip me off to finding these optimizations.
If you start paying attention to these things, you’ll find that your app becomes much more advanced user friendly and as a result it’s more accessible.