Using NFS between two machines on the same network is usually free of hassle, so the default behaviour – on Linux, at least – is fine and can be left as it is. However, in a commercial setting (such as the ones I manage in my day job) it’s often the case that the machines might not be on the same network – or even in the same location, for that matter. It’s likely that there’s a number of network devices in between the machines, and the way NFS uses portmap can sometimes make things frustrating.
Luckily, it’s really easy to fix.