Measured in watts, power isn't merely another word for volume. It also determines a receiver's ability to deliver detailed and dynamic sound. Indeed, a high-wattage receiver provides better sound quality than one with less power, even at low and medium volumes.
It's important that the receiver be powerful enough to accommodate both the speakers to which it's connected and the room in which the receiver is located. The power needed to match specific speakers depends on speaker sensitivity: the number of decibels (volume) it puts out per watt of power. Lower sensitivity speakers require more power. Additionally, the larger the room in which an entertainment system is set up, the more power needed [source: Bar].