As in code is better to manage in general compared to images in most parts. Could hotswap, could use variables, easier to maintain with a repo. Not to mention the ability to make themes easier.

There are just benefits, the downside is CPU cycles. But as performance improves with each iPhone, this is now negligible.

Fewer images loaded might lead to less memory in use and less load time which could lead to faster apps though..

Not true. Code based design is heavy on the CPU and not as fast as images. The part of load time might be true, but in general image based design is easier on the CPU.

Images run under cache. So images that are not currently in use usually get purged. Not using images because of memory is not a good idea.

You're probably right, but do you know of any heavily textured apps that suffer from slowness?

iOS apps don't use much more images than they did back in 2008, but the iPhone 5 has a lot more memory than the iPhone 3GS did.

It also has a faster CPU which makes code based design perform better. That was the downsides pre iPhone 4, slow cpu made images necessary. Memory has yet to be concern. So not using images because of memory concerns is a bad idea.