There are two scenarios. In one, you control the build process yourself, in which case nothing is physically stopping you. There is still value in doing it, because we are irrational creatures. We may be more likely to let a "warning" slide, rather than an "error," even though it is only classified as an error because we told it to do so. Being irrational creatures, we are loathe to go back on past decisions, and turning an "error" back into a "warning" requires action on our part that implies we were wrong before. We're more likely to just fix the "error."

The second situation is when you don't control the build process, in which case someone or someones are keeping you honest.