It doesn’t make much difference regarding your room size unless it is a small bedroom. However, 4 inches can make a difference to couples, particularly to those who are particularly tall in height. Check your own bedroom and use a rule to determine the difference an extra 4 inches in width or length would make. Many couples tend to prefer more width in their bed, while taller people tend to prefer more length, so that their feet don’t stick out of the end of the bed. You can check it by marking out the perimeters of a king bed vs a California king bed on your floor then lying out on the floor and deciding which would be best for you.