be setup for 1 node jobs.  Here are some of the reasons from IBM...

1. PE expects it.
2. For failover, if there was some challenge or difficulty with the
   shared-memory method of data transfer, the protocol stack might
   want to go through the adapter instead.
3. For flexibility, the protocol stack might want to be able to transfer
   data using some variable combination of shared memory and adapter-based
   communication, and
4. Possibly most important, for overall performance, it might be that
   bandwidth or efficiency (BW per CPU cycles) might be better using the
   adapter resources.  (An obvious case is for large messages, it might
   require a lot fewer CPU cycles to program the DMA engines on the
   adapter to move data between tasks, rather than depend on the CPU
   to move the data with loads and stores, or page re-mapping -- and
   a DMA engine might actually move the data more quickly, if it's well
   integrated with the memory system, as it is in the P775 case.)