In short: Nest has updated its app to allow users to enable the motion sensors that are part of Nest Secure, while the user is home. One of the use-cases that Nest provides in its YouTube tutorial on how to set this up, is being able to set motion sensors to on downstairs when you are upstairs sleeping. This can be useful if you get up in the middle of the night to use the bathroom, and the sensors are able to turn on lights for you, so you don't walk into walls and such.
Background: Previously, Nest Secure's Motion Sensors only worked when the user was "Away". This would allow the user to "secure" their home while they are away and get a notification while they are not home, when someone opens a door or a window. As these sensors were really only here to alert the user to when the door or window was opened, it didn't need to be on when the user was Home. Nest received quite a bit of feedback from users in this regard, and thus have opened up the motion sensors to work while the user is home. Nest likely saw many use-cases for making this a possibility. And now, thanks to an update from the Nest app - available on Google Play - users can do just that.
The impact: This is going to make the home a bit more smart and automated. For those that have larger homes and multi-story houses, this can be very useful. It would also let customers know when their kids come home (past their curfew) and there's not much the kids can do to sneak in as the motion sensors would still catch them. It's a pretty neat feature to add to the motion sensors, and may make many people pick up a few more for the rest of the windows and doors in their home.