In regards to your example:
All access to a system/network/forest/thing that contains secure data, must be kept secure from end to end, no matter how small the end is.
In regards to security in general:
All access to a system/network/forest/thing that contains secure data, must be kept secure.
There's a reason for this. A single access point to a network that contains secure data, is itself in need of security. Information of what has happened on the system as a WHOLE must be secure to keep the secure data all the way in the smallest part secure. If a single link in the chain breaks, the chain is broken.
But how do I break that chain if there is no security information on the client?
Simple, by observing the network. If I can see what goes on in the network, I can learn what keys will get me through what locks, how, and in what ways. Then I have an easy way to get into your network, and get your data. That is why, from end to end, ALL activity must be kept secure.
Let's go to the example of punching you in the face:
- You think your home is secure.
- You have bio metric finger print scanners(LIKE ON TV) that mean only your fingers get you inside
- You touch a door knob on a store front 70 million miles away, six years ago
- I lift that print
- I identify your print(through some long drawn out process)
- I use that print to open your home while you sleep
- I punch you in the face
Even though it was miles away, and that print had many other prints, and so forth and on wards, I could still eventually find your print in there, and use it to open your home. This is very improbable, but if I REALLY want to, I can still punch you in the face with time, effort, and some patience.
Still though this doesn't do more than present an example. Let's instead state the truth of security:
The most secure system in the world in buried underground, in an unknown location, burnt to a crisp, and destroyed.
Sure that's a little tongue in cheek, but it gets the idea across. So yes this security best practice should still be used. After all your system isn't the most secure system in the world, so you should try and get close.