This software provides multiple services to other applications: Location from wifi signals (via Google Location Service), sending and receiving unified push notification (via Google Push Messenging), making silent day appllications, etc ...
Many software packages depend on it. All Google applications (YouTube, GooglePlay, Hangout, Maps, etc ...) but also many third party applications that, to work (retrieve the position of the user, receive push notifications, etc ...), will be based on a service which is present on almost all Android: GooglePlayServices.
Behind this practical aspect, Google has its cornerstone need to control the Android ecosystem. Manufacturers are required to preinstall for the right to sell Android devices! It is necessary to access the main source software: GooglePlay.
Its source code and are operating remain opaque. The software has a permanent connection to Google's servers. Data exchanges are encrypted and made you can not have knowledge. Its installation must be done before starting the system because the software takes control of your system and runs as root (otherwise it could not make up for silent day for example).
Google can therefore, permanently and without delay, delete, modify, install or run what he wants on your smartphone without your consent. (but you could have guessed when Google told you that you could erase your smartphone remote ..)
Further, the permanent connection refers to your position at any time Google soon as possible, even when your wifi is turned off.
This should already rebelling. But the funny thing is that this permanent data flow pump with Google to death on your battery, even in standby. It's beautiful, you buy an expensive smartphone and Google spends your battery to spy on you, haha. By removing GooglePlayServices, you will increase your range of about 1/3. Just that.
I have a Samsung Galaxy S3 has 3 years now and I want 48H in daily use (use about 2/3 hours per day: RSS, email, web, chat, and video) and I do not put out the night. If I use it rarely me in the day between morning and evening, I lost only 25% of battery: p. And uncompromising (I have a sychro contacts / calendar. A Jabber messaging, receiving emails in push notification ....)
Unfortunately GooglePlayServices does not remove a click as you may have read. To my knowledge, you have to reinstall a virgin like Cyanogen ROM and therefore do not install the Google Apps.
To replace GooglePlay as source software, you Fdroid that contains only free software (spyware guaranteed, and rarely related to online services Again. CPU consumption and reduced radio)
And if you lack software available only on GooglePlay, you can download the APK format from my GooglePlayDownloader software (Linux must be good ... that's another story)