Tube power amplifier circuits are designed to work in harmony with a specific speaker impedance to achieve nominal function. With an impedance that exceeds the stated acceptable range (typically no greater than 32 ohms), the amplifier's output transformer or tubes can overheat and become permanently damaged.
Like tube amplifiers, solid state amplifiers are designed to work in harmony with a stated range of output impedance loads. Introducing higher impedances than the stated specifications will cause the amplifier to burn out its own power section over time and will permanently damage the amplifier.
Digital switching amplifiers amplify audio signals in a totally different manner than solid state or tube amps but are bound by the same impedance matching needs of balanced circuitry. Introducing impedances higher than the specified tolerances will cause damage to these amplifiers over the long term, and they will suffer from a lack of power and sound quality in the short term.