If done right, I prefer the look of complementing jacket and waistcoat not of the same color or cloth, IMHO, it makes an outfit while looking pleasant and ?gentlemanly?, also looks like the person wears a slightly more formal daywear attire often, also, occasionally always matching jacket and waistcoat screams of 'it's the only suit I have to wear.'
Also to clarify, sadly, I don't have the ability to co-ordinate that look which may be why I like it.