I've been having problems with memory management while using RenderScript, so I figured that since
The finalizer of Allocation will reclaim the memories when GC happens.
However, yes, it is a good practice to destroy Allocations when you don't need them any more.
One comment: it is usually a good practice to call Allocation.createFromBitmap(RenderScript rs, Bitmap b) when creating Allocations from a bitmap. It would make the Allocation share the data with the bitmap, thus you don't need to copy back and forth, as long as the stride of the bitmap is aligned on a 32bytes or 16bytes boundary.