It was a dark and stormy night...
Although the line was penned by Edward Bulwer-Lytton, it is probably most noted as the Peanut's character, Snoopy's first line attempt at a novel. It is also considered "purple prose, something written so extravagant, flowery or ornately to draw attention to itself.
Still, it establishes the ambiance of the story and the reader is aware of the outside weather to the story. Is that important?
Maybe yes, maybe no.
A descriptive sentence but what have you learned? Let's give it a little more detail.
Now we have a little more detail. We now know the room is a library and notice, by changing "walked" to "toddled" — we now have a better idea of the woman's gait? Also, the furniture upgraded from a couch to a "divan. Let's give it one more try.
Again, more detail. Okay, this is definitely pushing the edge on "purple prose" but I giving examples of how to expand your creative ambiance. The library is now mahogany-walled and the ladies are now "sipping" their tea and, if you noticed, the friends are socialites, not the neighbors.
I have been one to write my first pass using dialog to drive the story. I see the setting in my mind's eye but I don't put any of the details in the rough pass. When I go back to do the first edits, I add the ambiance. Doing very much what you just read above.
I originally wrote:
Now this is what finally appeared in the novel.
Maybe it pushed the "purple prose" limit, but, in your mind's eye, as the reader, you could see the lush growth of a hidden Brazilian grotto. This is a scene from "Ancient Blood: The Amazon."
Another example … I originally wrote:
This is what made the final cut into the novel …
In the above examples, notice how the expanded version added more ambiance to the story. It allows the reader enough detail to fill in the blanks and keep them in track with my vision. As a writer, it is critical you allow the reader some variance but, at the same time, you need to keep the reader on the same path as you.
If you describe dark eyes, don't blow it in the next paragraph or chapter with "light blue" eyes. No matter how hard you try, light blue is never going to be dark. They can be brooding, but that's another description.
Remember, one man's grotto is another man's cave … or was that garbage and treasure?