It's good when dealing with humans, it's bad when dealing with machines. Allow humans a fudge factor for ease of use, but not at the cost of integrity. For in

It's good when dealing with humans, it's bad when dealing with machines. Allow humans a fudge factor for ease of use, but not at the cost of integrity. For instance, allow phone numbers with separators, or spacing, or shortened versions etc. It's aggravating when a form asks for a cc number and allows a user to type spaces but the field has a max length so you have to backtrack and delete all the spaces. Make apis conservative in what they accept. This reduces complexity and the likelihood of bugs.