Memory bandwidth in mobile devices is very restricted compared to GPUs in desktop systems. It can easily become a bottleneck limiting the performance of your application. For this reason, try to minimize your use of memory bandwidth:
Bandwidth is a shared resource so using too much can limit the performance of the entire system in unpredictable ways. For example, graphics memory is shared with application memory so high bandwidth usage by the GPU can degrade application processor performance.
Accessing external memory requires a lot of power so reducing bandwidth usage reduces power consumption.
Accessing data in cache reduces power usage and can increase performance. If your application must read from memory a lot, use techniques such as mipmapping and texture compression to ensure your data is cache friendly. See Use mipmapping, and see Use texture compression.
Determining that memory bandwidth is causing problems is difficult. See Determining if memory bandwidth is the problem.