A test by a reddit user found that removing the Facebook app and the Facebook Messenger app from Android phones made the phone launch other apps on the phone 15% faster. Other redditors also reported similar results.
A reporter for The Guardian found that removing just the FB app saved 20% of his battery life. He replaced the app with Metal, which still let him access Facebook.
Does it really make this much difference if you already close the app so that it's not running in the background all the time?