While using Facebook login or Google login on any site or app you have to look at the permissions the website is asking to access your data. Only you can allow this. If you are allowing permission to post on your behalf then an application or website can post on your timeline. Likewise, messages, posting on pages, managing friend lists, etc also need your permission for a website to access the same. Some sites need only basic information for login puposes. For eg: Answeree.com is only asking for information about your name, email, and profile picture in order to create a profile here on Answeree. Other than that we don't have any access to your social media account, profile, or data. In such cases, you are good to go with social login. It's easy and convenient.