Why should you buy a power amplifier, which in most cases means that you also have to buy a preamplifier, when you can instead buy an integrated amplifier that may be cheaper? Buying a power amplifier can be the easy and cheap upgrade to get more power and good sound to the speakers, if you have low-level output from your stereo amplifier/receiver. There is also a flexibility to run separately where you can change individual components in the chain, for upgrading or perhaps to change the character of the sound. Then there is often a sonic advantage in separating the components, so the powerful final stage does not interfere with the sensitive preamplifier. It is for a reason that the best sounding systems have separated components.