It's for private photo sharing with family or close friends. It's more like an open-source, self-hostable TinyBeans or PhotoCircle. I explain the motivation more in the design doc:
The target audience of the app is me and my wife. This is a "home-cooked meal" app.[0] If it's useful to other people, I'm glad, but I'm primarily building it for myself for the pleasure of building and the satisfaction of a tool that works exactly how I want it to work.
You could approximate it with email, but I want things that you can't do with email like letting recipients control the frequency of emails, making high-res images available without bloating everyone's inboxes.