This is true for lots of apps. For example I don't use the Gmail app nor any other mail app for iOS because the sync traffic kills the battery. I just use Gma

This is true for lots of apps. For example I don't use the Gmail app nor any other mail app for iOS because the sync traffic kills the battery. I just use Gmail's excellent mobile web site, which also means I don't get interrupted by notifications and I read my email at the time and place of my own choosing. Calendar is another battery killer. I found that I can use calendar apps but I can't sync the calendars of middle managers at work because all they do all day long is attend meetings and fiddle with their schedules, and again the sync traffic clobbers the battery. But if I just sync my own calendars it doesn't seem to matter. I wonder if the Facebook battery usage is proportional to how many friends you have in your network, of if it just uses a lot of energy regardless.