Constraints make sure users not make mistakes by simply limiting the range of fields users are allowed to do. It helps users to manipulate the system efficiently. For example, for entering a date, an interface can have set dates that users can choose from instead of inputting things themselves, which can have high user error. Another example is constraining how users fill out credit card information.
Contributed by Jason Thong, Xiao Zhang, and Deedee Jiang