like consider for example the strictly functional line:
Suzi was very nervous.
okay, weak sentence, we all see it. plain structure and plain descriptors. so you spice it up by using some figurative language:
Suzi had butterflies in her stomach.
this is stronger! but still not much better; you write this and can tell it suffers from being an overused idiom. so your next instinct is to say, "well, then i'll just elaborate with some more interesting language!" and so you modify it into:
Suzi had butterflies in her stomach. She was absolutely sick with worry, terrified of what might happen, too frightened to speak— or even breathe.
again, stronger, but counterintuitively, you have made the idiom weaker by explaining it.
"butterflies in her stomach" now does nothing for the experience of the reader but add a cute little touch of aesthetic flair without actually carrying any of the weight of communicating how suzi is feeling, because you immediately told us how suzi is feeling.
try expanding the metaphor instead:
Suzi had butterflies churning in her stomach, crawling up her throat, cluttering her lungs, and sticking all over the inside of her mouth. Forget speaking— she could barely even breathe.
now THAT'S an expanded metaphor! the cliched idiom becomes refreshed with the vivid descriptions, and the gravity/specificity of suzi's tongue-tied anxiety is communicated without being explicitly stated. the idiom may even make the reader vicariously feel what suzi feels with how graphic the description is, intensifying the tone of distress and discomfort.
and this goes for any tone and any metaphor. expand a frightening metaphor by making it gorier and gooier; expand a funny metaphor by dialing up the slapstick. but above all, TRUST your audience. you don't have to say everything perfectly clearly... and sometimes it's more effective just to paint a picture and let that do the talking.