Purpose of Reference Atlas?

[DevMan5000]

https://www.youtube.com/watch?v=dbwgP6PC4go

I watched the link above which explains references atlases.

Is their purpose to reduce the run-time memory footprint and reduce the number of pixels being processed on lower end devices (thus increasing performance)?

If I ship a game with multiple versions of the same atlas (SD, HD, ultra HD), then those textures are all going to take up hard disk space, so that actually is a negative because it increases the app's size.

My plan for my story book app was to just make one atlas with everything at iPad 4 size and then let NGUI just scale all the elements down for iPhone4, iPhone5, iPad2, iPad3, iPadMini.

My app is pretty simplistic (background image and text on each page) so I'm thinking perf won't be a huge problem.

Is there a good reason why I should abandon my plan and go with reference atlases?

[Nicki]

References atlases are there to facilitate multiple sized atlases, if you must have pixel perfect on many or all devices. If you don't need this, just run with a single atlas, since the unused ones are just that. They won't be in memory though, which can be nice for low end devices.

[DevMan5000]

Ok, thanks for your explanation. I am somewhat of a noob in Unity, but based on my UI experience, maintaining multiple atlases seems like it would open the door for a lot of bugs. E.g. "oh I forgot to update the sprite on the other atlases when I made that character change."

Ideally, the UI can just scale down appropriately and work on all the devices that I am targeting, without additional specialization. I'm hoping that will look fine on smaller devices.