what you can use it for:
Is messenger safe?
Despite what you’ve heard, Facebook’s Messenger app isn’t going to call or message your friends or use your device’s camera to see what you’re up to. For one thing, Facebook would get into HUGE trouble if it did, and it wouldn’t be tricky to catch Facebook in the act, particularly after all of this bad publicity highlighting such privacy issues.
The app does not give Facebook “direct control over your mobile device,”
In fact the Messenger app’s permissions aren’t much different from the main Facebook app that you’ve been using for years, and there are probably several other apps with almost identical permissions installed on your device already.
On Android, downloaders of the Messenger app have to agree to give Facebook permission to access the device’s camera, microphone, contacts, location, calendar, WiFi information and more, which does seem rather daunting.
So, while it is pretty annoying that Facebook wants us all to download the Messenger app (we all hate change, but we’ll get used to it), don’t let scaremongers put you off of downloading and using the app. All apps come with privacy concerns of one kind or another and Facebook Messenger is no different, but it’s not going to spy on you and it’s not going to send messages to your friends or call your family without you knowing.