Writers often hear advice from published authors and teachers that are taken for granted. One is "show don't tell" and another is to never use adjectives and adverbs. Most writing advice that has become axiomatic is valid, but too often we hear the axiom but not the truth it is based on.
Lean, Powerful Prose
The fewer words you use, the more powerful your sentences are. The word "steak" is much more concise and powerful than "a great big piece of meat". The more you say in fewest amount of words the more you communicate in a shorter amount of time which will result in a greater impact. Often we get caught up in specifics that are only objective observations that do not hold much meaning for others. You might think your character "whispered daintily" but is it really worth watering down your prose for that. Whispers are always dainty.
Specific Images, Actions
Using single words to describe actions and objects quickly brings them to mind. When someone "stabs" a straw into their drink we see it, but "pokes swiftly" is not so clear. When a person "meanders" it is more accurate than "walking slowly". A man whose foot is described as a "hoof" is much more vivid that having "gnarled toes and sole". A "Porsche" is a much more striking image than a "German sports car".
Would A Character or Narrator Use That Word?
People do not use a lot of words. More often than not they err on the side of too few words. Only very particular narrators will so verbose as to use many extra words like adverbs or adjectives, your narrator probably is not that guy. Internal monologues will be filled with shorthand, not much use for extra descriptive words. In dialogue we use the most oblique phrasing possible, only getting specific when forced to.
Too Much Unnecessary Text Induces Skipping
Before the movies were invented people must have liked flowery over-the-top prose. They must have loved reading two pages of what someone's nose looked like, but these days people want you to communicate something meaningful at all times or they will take things into their own hands. As much as you might wish people to read every word you write because since it came from your head you feel it's important, if it is not relevant to the story or their life they will skip a bit... then some more... then maybe stop reading altogether. Test them at your peril.
Using Only Necessary Words Instills Trust
When a writer shows discipline in prose, they will be rewarded with attention when they do take time to explain more in-depth or to describe more fully. The mere fact that a prudent writer makes a point of deviating from their usual course of prudence shows that it is important and the reader will feel it and appreciate it. If you value a reader's time and attention they will value your taste and craft.
You need not be as sparse as Hemingway but in that general direction you ought sway. As writers we do think everything we write is important and it *is*; though that importance may only pertain to ourselves. When we write you have to keep the other in mind, it is like we are having a dialogue where the other person is mostly silent and answers back by continuing to read. You can never know what will turn someone off but you can do yourself a favor by packing the most in the least and that is why you should avoid adverbs and adjectives as much as possible.