Power conditioner will ensure incoming voltage is within range, so it will protect your amp from surge and peaks, plus RF (Radio Frequency) filtering. Mine also has voltmeter and ammeter ... so this way I know what is going on in a certain situation.
Just imagine you are on some stage running your amp on some questionable generators and on the same phase light guy is switching on and off some big lights (kW)... that is bound to cause some voltage spikes. Things like that power conditioner will take care of... for more, you need a Voltage Regulator but like hywelg said, that stuff is expensive.