I work as a mobile developer for 2 years, which is not much. But I develop the application for server-client voice calls. And for several reasons we can't use popular frameworks to maintain calls, so we have to write our own algorithms for sound processing and connection maintaining. This actually demands some math and algorithms knowledge.

Also, I work on a mid-load server application, which also demands some knowledge about data structures and algorithms, as I have to process tens of thousands of elements as quick as possible.

Finally, I have seen guys writing really slow algorithms, although there were simple and much faster solutions that demand only a small piece of data structures knowledge. And you don't have to process large amounts of data to notice the difference. If you can make your UI half a second faster - that's enough for users to notice the difference.

I don't say that you have to burry yourself in algorithms and math books. I know, that you also have to understand the frameworks you work with and debugging, and testing and tons of other stuff. I just think that math and algorithms could and will make your work easier if you know at least some basics. I'm pretty sure you will never need Fibonacci heaps and B-trees, but using linked lists or hash maps instead of arrays sometimes can really help you.