You may not be aware of it, but you probably use Google Play Services every single day you touch your Android device. Not directly, but in the background as it's pretty much baked in to many different areas of the Android operating system and it's essentially the backbone of all your Google apps. A lot of what it has to do with is mostly for the developer side of things, so they have an easier time working with their apps and integrating new changes. There are some direct user side functions for Google Play Services however, and a couple of new ones are worth highlighting in this most recent update to the apk which brings it forward to version 7.3.
First and foremost, Google Play Services technically got its update earier this week, but updates don't always make their way to everyone on the exact day they're pushed out by Google, as is the case with this here. The first change is something that will likely please anyone who owns a Moto 360 or any other Android Wear smartwatch. With Play Services 7.3 you can now dismiss the persistent notification that would sit idly in your status bar on your smartphone. This probably didn't bother everyone, but many more than likely hate having anything more than what's needed in the status bar to begin with, so this is a very welcomed change.
The second change to point out is that Google tweaked the user interface for Trusted Places. If you add a new trusted place or edit an existing one, you'll be able to see a handy little map that shows you where you've designated your safe zone for a trusted place, and it's even further emphasized by a blue dotted ring that surrounds the area. This should help to make it extra clear as to exactly where your safe zone(s) are with much less confusion, and less confusion is a good thing. This should be continuing to roll out to people over the weekend if you haven't already gotten it since the update started, and if you are still waiting but want the update asap, you can grab the APK link here to update the apk manually.