The difference between using text and icons for interfaces is that icons are clear to new users only if they are immediately identifiable. With universal things

The difference between using text and icons for interfaces is that icons are clear to new users only if they are immediately identifiable. With universal things like email, that's easier to do; for example, the user knows there must be a "send" button and so immediately recognizes an arrow button. When the user needs to learn the interface (more generally, the mode of interaction), icons are harder to use effectively.