[sratner]

No memory allocation/reallocation, preallocated resources managed in e.g. a free list. Also for things like packetized networks, lists are handy for filling as you progress down the stack while using fixed sized packet buffers, or reassembling fragments.

In embedded world, memory often needs to be exactly controlled, and allocation failures are fatal without a more complex MMU. In kernel world, I believe the main reason is that allocations can block.