With the release of the Android M developer previews and soon to be the final release of the next version of Android software known as Android 6.0 Marshmallow, users will have a new way to interact with permissions for apps. Instead of being required to grant permissions to apps upon the installation, users will be asked to grant the app permissions after they open it up for the first time. Short of being what feels like a better way to do things, it will also likely make users feel a little more secure about app permissions as they won't need to grant them immediately.
With the latest release of the developer preview which at this point is version 3 (and it could be the last preview build before Google eventually launches Android Marshmallow) it seems Google is changing things with floating applications. For those who are unaware, floating applications are apps installed on the device which can be drawn on top of the screen when other apps are already open, like Facebook's Messenger with the chat heads, Link Bubble, or any number of other apps which allow users to interact with apps while they're already using another. The changes in question are such that going forward, users will need to grant permission to apps that are requesting to float on top of the screen. This is already present in the Android M Dev Preview 3, and could very well stay once the official release of Android 6.0 Marshmallow hits.
With this new permission for floating app requests, users will see a notification pop up asking them to navigate to the settings menu where they can access advanced options, and finally "draw on other apps" where there will be a list of apps that have this capability. Toggles will be listed for each app, and users will have the ability to turn them on or off as they please, but the toggle will need to be enabled if users want any apps to be able to draw on top of others. Once permission is granted for the floating app function, users won't be asked to grant it again, presumably unless they decide to ever disable it, at which point they may end up seeing the prompt appear once again in the notification tray.
At the moment Google hasn't mentioned any reason as to why they would change things up in this way, but it's suggested that it could be due to the high-risk nature of this particular permission type. In this regard it makes sense then, that Google would want users to be aware of what apps are asking for and give them the power to grant or deny this permission. From a user standpoint, this will end up giving them a little more control over various aspects of the software, just like with the permission dialogues that will be present in Marshmallow when you open an app for the first time. It's also worth noting that while apps may ask for permission to draw on top of other apps and users will have the capability to deny this request, doing so won't affect their ability to use that app. The floating function just won't be accessible, and it can be toggled on at any time.