
Chorus effect creates an illusion of multiple instruments playing at once. The effect is produced by splitting the original electric guitar signal, and than delaying and pitch shifting one (or more parts) of the signal that when combined together produces chorus effect.
Almost any rock balad song has a chorus effect on a clean guitar sound. It just sound so amazing when effect is applied properly. You should definetely have such a pedal in your arsenal,
you can check out the prices here.