I think often diminished and augmented chords are laid in there to embellish stuff. Not necessarily written as such in rock or country but often just put in there. One might go to a G7 at the end of a middle eight or chorus then go to a C to start the next verse or alternatively G7 , G+ then C. This rides up nice and rounds the end of the chorus. Sometimes works great even in rock but often it is not written.

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