What is the real difference?
The real difference is that images saved into the Watch App
are going to be installed on the Watch. Images saved into the Watch Extension
are going to be saved on the iOS device.
This is a VERY important distinction because it is very slow to add a cached image using the WKInterfaceDevice
APIs. Any static images for your Watch App MUST be stored in your Watch App and not your Watch Extension. Only dynamic images that are generated by the iOS App or Watch Extension should need to use the WKInterfaceDevice
caching APIs.
Is there any limit to app size?
Apple has not publicly posted any limits. One could speculate that there most likely is a limit.