Parking lots try to get cars to slow down.
The “policy” is that you should drive 5-10 miles per hour there, but some people race through it during tough commutes. That policy is usually written on a sign, with the expectation that people will read it, and naively hoping people will follow it.
Good design is way better than any policy. Enter the designer: don't put a sign, just put speed bumps on the road. Drivers knows what happens. You better slow down or your car's contents will bounce up and down. If you drive fast, you’ll almost certainly blow out your tires. No sign needed, no pleas, no police citations, no traffic cameras. Slow down or you’ll get a flat tire or two. Problem solved.
When something isn’t obvious, people tend to set a policy. “Any food not labeled will be thrown out on the last Friday of the month” - that’s the policy. It’s something you have to either know or be taught. It’s not obvious, and it’s not apparent just by opening the fridge. Policies are a pain. They get posted, reiterated, ignored. If everyone knows why all salespeople have to work on the Friday after Thanksgiving (if it’s the biggest sales day of your year) then you don’t need to mandate it. If everyone has an incentive to be there that day, even better.
Some companies try a “we trust our people to do the right thing” approach as a way to try to bypass the need for policies. If you have a truly great team of people, you may be able to achieve this just by staying out of their way. Larger companies don’t always have this luxury, so policies are added to preserve precious (and precarious) profit margins. Recent graduates with MBA's will determine that with a simple policy adjustment, money can be recouped, or saved, or shrinkage reduced. Employees will complain that things aren't fair or clear or obvious, so the "simple" thing is to just add a policy; except anything simple to create almost always adds complexity. Conversely, anything truly simplified often requires complex work to get there. A policy is like a scotch tape solution: it may work in the short-term but it won't hold long-term.
Employees need to wash their hands before returning from the restroom. You've likely seen this policy before. That's because there are few systems that could effectively enforce this without some obvious privacy violations. As a result, it's a weird sign that only impacts a small percentage of the restroom's visitors. Everyone sees it, and it's clumsy, awkward, and it's the law in many states.
"No shoes, no shirt, no service" is a policy, often accompanied by a sign. Also there because of laws, or municipal codes governing safety or food service cleanliness. Sometimes it's a community standard. Either way, it's awkward even if it does avoid the person behind the counter having to remind a customer of the rules.
A speed bump instead of a sign is a beautiful design. You can't ignore it. You can't "opt out" - you can disagree with it all you want, but it's not moving. It's completely enforced, simple, wordless. If your fast-food restaurant's policy is "one dipping sauce per customer", don't put that on a sign. Just put "first dipping sauce is FREE!" - that's not a policy, that's a benefit. Then put the other dipping sauce prices on the menu, just like the other food. Then it's not a policy, it's just another food item.
Simply put, policies are design failures. If you need to clarify something with a policy, you’ve effectively failed in designing something that employs simplicity and intuition. Some policies are in place because even with reasonable design, people sometimes try to take advantage.
If you can avoid a policy by making something simpler, do it.