using idioms can make your writing and speech feel more natural / easier to follow / crystal clear

instead of using long or flat phrases, you can say the same thing in a more vivid way
for example, “cut to the chase” can replace “get to the point,” and “hit the nail on the head” can replace “explain it exactly”
the meaning stays clear but the line feels sharper and this helps because it removes dull wording while keeping your message strong
it also sounds more like how people speak which makes it easier for others to connect with what you say
putting it in a nutshell, the more you use idioms well, the more your vocabulary grows / expands in practical way