Negative space can be a powerful design tool. When used correctly, it brings a sense of calm to a space and actually puts the objects that are in the space into focus by drawing the eye toward it. The act of well-done negative space is accomplished when someone understands the importance of editing. In design, not every space always needs to be filled in order for the room to feel finished but understanding when there's something missing and when enough is enough is a delicate balance.
Negative space works well when done right because it eliminates all of the distractions. Oftentimes, it is a much more simplified version of layering and requires the viewer to step back and look at the space as a whole...even though, ironically, it brings items into focus.
Negative space oftentimes thrives where asymmetry is present because whomever has accomplished the use of negative space has looked at the space as a big picture. It sees the room as one pictures instead of becoming hyper focus on filling things up. Wall space and ceiling space is seen as the backdrop for everything in the room so the way pieces of furniture in the middle of the room stand off the back wall affect what else is hung on the wall and where.
Negative can often be used to emphasize architectural details like windows and stairs but be careful because sometimes it can also highlight things you might not want in focus. Just be sure your furniture doesn't detract from architectural details you might want to highlight...it's ok not to crowd a room with furniture if it keeps the cool architectural details in focus.
If you're still unsure about the benefits of negative space, just think about a bold black and white patterned tile or wallpaper or even fabric. The black portion is the negative space and without it, there is no pattern! Negative space is important! Be sure that you're stepping back to look at the big picture each time to re-design your space.