It is easy to deride the humble cliché. Some people suggest that every use of a cliché is somehow wrong, or else it demonstrates a sad degree of laziness on the part of the speaker. A weed, as my schoolmaster used to say, is simply a plant in the wrong place; and a cliché can be a phrase in the wrong place - but then again, it can be gloriously right and appropriate.
Imagine I am writing a story. The hero is honest and straightforward: he says 'now'. The protagonist is a pompous windbag, as you can tell when he says 'at this moment in time'. The choice of when and where to use a cliché says a great deal about our character and background - it tells people about who we are.
Or imagine at work we have an important decision to make. It involves some risk, and there is a temptation to put off making it. I say that we must 'grasp the nettle'. It is a simple, effective phrase which conveys a clear meaning. We can all understand and relate to the image, and the metaphor is direct and appropriate. A picture says a thousand words, and these three words paint a picture which communicates a truth about our situation, and communicates this truth on several levels.
What are the alternatives to 'grasp the nettle'? You can 'grasp the opportunity', but that misses the element of risk. You can 'take the risk', but that implies the hearer is hesitating out of cowardice. You can pinch, hold or squeeze the nettle, but none are as dynamic as 'grasp', and each of them raises a doubt in the hearer about what the speaker is intending to imply.
Another point often missed is our tremendous capacity for irony. Clichés like 'to coin a phrase' inject an ironic and self depreciating note into the conversation. Sometimes it means: I know what I am about to say is hackneyed, but I can't find a better way to say it. In other cases, the irony raises itself to the level of a Public Health Warning: when I say 'to be perfectly honest...' I am telling the hearer to be careful. What follows may not be the whole truth, or it may be truth that you will find unpleasant.
As with all language, clichés can be used carelessly and ineffectively, but many of them have associations and resonances which ideally suit them for particular purposes. Even if there were no other advantage, they are familiar and non-threatening, so if I want to communicate in language which is familiar and non-threatening, they can deliver the desired tone in a gentle and graceful way.