To this day I have still never found any application on any device that is as simple and easy to add an arrow and some red text to an image for highlighting something as it is with preview. It is just unbelievable how janky and bad every single other application is at doing this simple task. Not even on phones is there anything easy.
Ahh interesting point. Somebody needs to make their next 20% project a gmail labs extension that gives a simple annotate option to images in mail. It would probably be a sleeper hit that gets more use than 90% of other gmail features.