All men should own at least one waistcoat for dressing up in, and that doesn’t imply that said waistcoat should only come out once in a blue moon.
A decent waistcoat can add a bit of flare to almost any outfit. Take the humble grandad shirt. Comfortable and worthy for a jaunt to the pub, but that’s about it. Add a waistcoat and a pair of trousers in a similar colour and you’d look smart enough for an introduction to any girl’s (or boy’s) parents without looking like you’re trying too hard.