In some cases, building Propellor on the target machine is undesireable; for example, the host has limited memory available, or the load imposed by GHC on CPU / I/O usage is unacceptably disruptive to other services running on the host. When spinning from a compatible host, Propellor could instead have an option to copy the locally-built binary to the target host. I'm not sure exactly how to determine "compatible" in this case, so it would probably have to be left to the user to determine whether they can do it or not.