Constraints: The Good and The Bad
A Good Example of Constraints: The Harvard Lampoon Subscribe page
The web page to subscribe to the Harvard Lampoon magazine is an example of good use of constraints that allow that user to only submit valid responses when filling out the form to subscribe. For example, when you say that you want to give the subscription as a gift, the form is immediately altered so that you don’t get an account to the Lampoon (because the recipient of the gift would be making that themselves) and automatically creates fields to enter a billing address that is different from the shipping address (because the recipient of the gift will inherently have a shipping address that is different from the billing address of the person sending the gift). This way, the user cannot accidentally say the billing address is different from the shipping address or make an account that would be unnecessary or rejected by the system.
A Bad Example of Constraints: Harvard desk chairs
The back end of Harvard desk chairs move upward so that students can tilt back slightly in their chairs, but not so much so that they tip over. Yet unfortunately this example of constraints poses a binary for students: either upright or very slightly tipped over. It gives the students no option to recline to their exact liking. So while there is a constraint imposed here, it is limited and ultimately compromises the experience of using this chair.
While the previous chair had a flat incline that allowed the chair to tilt in a prescribed way, this new incline is rounded with ridges so that there are different levels at which you can recline. These ridges control your recline so that you can be slightly reclined, slightly more reclined and fully reclined. It gives the user more options while still keeping them safe and within a constrained range of use.