Google Play Services helps to update Google Apps and update all other apps from Google Play. It runs in the background and checks the necessary updates you require. When you buy a new smartphone from the carrier, it comes with pre-loaded apps, but after installing Google Play services, you will be able to get all the latest updates for your specific model.
The app has 3.9 rating on Google Play, and so many people complain that the software eats up a lot of RAM and battery. Thus Google is continuously working on it to give it more stability. We have got a new update which certainly comes with more bugs fixes and improvements.