Every room needs balance, places for the eyes to focus, weight distributed throughout the room so it doesn't appear lopsided. Think of your room as a scale and always add a bit more to one side or the other so as not to tip it too much in one direction.
Let's say you have a room with a single, overwhelming focal point: a large fireplace or a large, dramatic window. If there was nothing else in the room, your eye would go directly to that spot. That's fine ”it gives you a starting point ”but it's not the only thing you want to see.
There are several approaches to balance.
Sometimes you need to enhance an architectural focal point. For example, a large window framed with draperies needs to be anchored with something of substance ”maybe a sofa or a pair of large chairs angled around a table. If not, that focal point seems too top heavy.