In most cases you will want the subject to stand out in your photo. There are several ways to accomplish this, with Negative space being one of them. In photography, negative space refers to the space surrounding your subject. The fewer the distractions in this area, the more your subject can stand out.
This space doesn’t have to be a blank wall though. Just as long as it’s not too busy to distract from your subject, it will do a good job in highlighting it. This also allows you to have an abundance of composition possibilities, giving you more creative freedom in how you present your subject to your viewers. If it’s a person, do you put him/her on the left, centre, or right of the frame? Will they be jumping or standing still? Will you try and focus on their expression or stand back to get the whole picture?
The key is to look for that large expanse of a backdrop that will allow your subject to shine on. Go ahead, try it out the next time you’re out shooting!