Android P enables accessibility services in the background so the user doesn't have to, and this results in a much more seamless experience across the board. (androidcentral.com)
For instance, before the introduction of the Autofill Framework in Android O as mentioned previously, password managers had to use Accessibility Services in order to detect when a valid password entry field is on screen. (xda-developers.com)
You do have to go through a few pages of settings, including enabling Accessibility Service for the app. (slashgear.com)