I encountered a really odd behaviour with my Raspberry Pi B+, running a slightly modified version of Raspbian with a PiTFT screen from Adafruit. Because the screen cannot access the GPU I dialed down the GPU memory as low as it would go during installation (4 MB I think?).
I wanted to use the system as a portable music player, but I found the audio playback was extremely poor (constant skipping). I tried changing the GPU memory split to 32 MB, and all of a sudden the playback was completely smooth.
I thought that the GPU was primarily used for handling calculations performed while rendering 3D graphics. Why would it affect audio playback this noticeably?