Idioms offer a way of expressing an idea that can be at once more interesting, colourful and concise than a more literal (compositional) expression of the same idea. We all use idioms, and language would be bleaker without them.
Cliches gain a foothold in language for precisely the same reasons as idioms: they present a way of expressing an idea that seems like an attractive alternative to other ways of expressing the same idea. The other ways may be a literal expression, or another phrase that, when it first appeared in the language, seemed to be a clever alternative to that literal expression but is now, alas, a cliche.
Source: Guardian
