In versions of Google Play services prior to 6.5, you had to compile the entire package of APIs into your app. In some cases, doing so made it more difficult to keep the number of methods in your app (including framework APIs, library methods, and your own code) under the 65,536 limit. From version 6.5, you can instead selectively compile Google Play service APIs into your app
inside compile com.google.android.gms:play-services:12.0.0 contains alot of dependencies.. see below.. using play-services may cause dex problem and heavy app. Select only which want do you really depends to 🙂
Google Play services API Description in build.gradle
Google+ com.google.android.gms:play-services-plus:12.0.0
Google Account Login com.google.android.gms:play-services-auth:12.0.0
Google Actions,
Base Client Library com.google.android.gms:play-services-base:12.0.0
Google Address API com.google.android.gms:play-services-identity:12.0.0
Google Analytics com.google.android.gms:play-services-analytics:12.0.0
Google Awareness com.google.android.gms:play-services-awareness:12.0.0
Google Cast com.google.android.gms:play-services-cast:12.0.0
Google Cloud Messaging com.google.android.gms:play-services-gcm:12.0.0
Google Drive com.google.android.gms:play-services-drive:12.0.0
Google Fit com.google.android.gms:play-services-fitness:12.0.0
Google Location and
Activity Recognition com.google.android.gms:play-services-location:12.0.0
Google Maps com.google.android.gms:play-services-maps:12.0.0
Google Mobile Ads com.google.android.gms:play-services-ads:12.0.0
Google Places com.google.android.gms:play-services-places:12.0.0
Mobile Vision com.google.android.gms:play-services-vision:12.0.0
Google Nearby com.google.android.gms:play-services-nearby:12.0.0
Google Panorama Viewer com.google.android.gms:play-services-panorama:12.0.0
Google Play Game com.google.android.gms:play-services-games:12.0.0
SafetyNet com.google.android.gms:play-services-safetynet:12.0.0
Android Pay com.google.android.gms:play-services-wallet:12.0.0
Android Wear com.google.android.gms:play-services-wearable:12.0.0
Firebase
Firebase API Description in build.gradle
Analytics com.google.firebase:firebase-core:12.0.0
Realtime Database com.google.firebase:firebase-database:12.0.0
Cloud Firestore com.google.firebase:firebase-firestore:12.0.0
Storage com.google.firebase:firebase-storage:12.0.0
Crash Reporting com.google.firebase:firebase-crash:12.0.0
Authentication com.google.firebase:firebase-auth:12.0.0
Cloud Messaging com.google.firebase:firebase-messaging:12.0.0
Remote Config com.google.firebase:firebase-config:12.0.0
Invites and
Dynamic Links com.google.firebase:firebase-invites:12.0.0
AdMob com.google.firebase:firebase-ads:12.0.0
App Indexing com.google.firebase:firebase-appindexing:12.0.0
Performance Monitoring com.google.firebase:firebase-perf:12.0.0
EDIT
Above version is already deprecated. They use individual versioning. Please refer Link Below
Google Play Service – https://developers.google.com/android/guides/setup
Firebase – https://firebase.google.com/docs/android/setup