Description is a vital part of fiction writing. How much description to include depends on the type of story and the audience, but what type of description and the choice of language depends upon the viewpoint character.
Three different characters see the same room in different ways. What they notice and don’t notice, and the words they use to describe it, vary according to their background.
The reader gets a sense not only of the room, but the character as well.
The point of the descriptive exercises is to practice putting a character’s slant on what you describe in your story. Unless you use a totally omniscient point of view, what you include in the description will depend on what is important to your character.
For another type of practice, read Descriptive Writing Exercises and Character Voice Writing Exercises.