With that said, I always lock my computer out of habit.
If so, I would hope the responsibility for setting opsec policy isn't resting in one sysadmin.
Or more prosaically, do you have any semi-confidential e-mail on your machine, that a coworker might fancy reading?
It's all a series of defenses, the last one you should ever rely on is piecing together what happened by video camera... what happens when they install a root user, or ssh authorized key on your system and then do whatever they want at some other time?
This is a fire-able offense where I work.
Barring myself from working at an company with more than ~150 people (Dunbar's number) because I'm too pompous to lock my laptop doesn't seem like a metric one would be wise to follow.
This is like bricking up all your windows against thieves when you live in sleepy, low-crime suburbia.
Site security needs to have a balance between paranoia and practicality. For public-facing code, history has shown us that it's impossible to be too paranoid. If you work in national security, or your industry is known to be a target for industrial espionage, then certainly strong precautions are in order.
But if you're just building social media sites or whatever, and you're firing people because they failed to stand ever vigilant against the possibility that Bob the visiting vendor rep might stalk the corridors waiting for you to take a bathroom break so he can rifle through your code for exploits to sell to teh haxxorz, you are being absurd.