If you connect your amplifier to the wrong speaker impedance, you risk damaging the amp. In tube amps, too high a load impedance (or a disconnected load) can result in damage to the output tubes or output transformer, while in solid state amps, if the speaker impedance is too low, the amplifier will tend to overheat and more power is used up in the amplifier than is delivered to the speaker. Too many speakers on a solid state amp can burn up the power output section.