For me I've been less certain. As I've mentioned on the odd occasion I could do with losing a bit of weight. This, I thought, might be masked a bit if I bought a waistcoat with what was my third tailored suit (the first was a bit of a mistake, the second was OK if a little conservative - I wanted another for formal wear) then it would all tone in and I might look a little smaller.
This might, indeed, have worked. That's if I hadn't done the classic thing of thinking fewer buttons would be better, so I want for a four-button jobbie. This meant a dark suit against (usually) a white shirt, waistcoat tapering to a point just about where the ribcage stops and the gut begins. In other words it was as if there was a great big white arrow pointing to the belly area.
I've had more success with a six-button version on another suit. Nonetheless I can recommend them as a good look for dressy occasions, probably for smaller-waisted men. A Suit That Fits is giving away waistcoats with suits to people on its mailing list; click that link (it's sponsored, I get loyalty points for clicks but you're not obliged to buy anything), sign up for the newsletter and assuming you get this week's there will be instructions on how to get a free waistcoat when you buy a new suit.
I won't be doing it myself. Partly because I have enough suits but mostly because I look better in a two-piece.