Anonymous SHared Memory
Large application needs to cache expensive operations. But, these operations are _less_ expensive than swapping and less expensive than if the app got, for instance, OOM-killed. The Android browser uses this to store decompressed images so it can draw them to the screen. It can always decompress them again, and a swapped-out decompressed image is pretty worthless.
Obviously contrived example: "grep" could keep the results of a grep through a large file in an ashmem cache. If you did the same grep twice, you could return the cached result instead of reading the large file again.
This kind of use does not fit well with a model where VMAs are used to track volatility. There generally is not a VMA around since the program only runs for a short time. If a VMA would be required to indicate the reclaim state of a page, then it could not be reclaimed most of the time.