The three piece suit is a commitment that most modern men make only for very specific occasions and that specific occasion quality is actually part of what makes it so effective when deployed correctly. It reads as significantly more formal and more deliberate than a two piece and that formality commands attention in situations where that’s what you want. The waistcoat does particular work for men who find jacket sleeves slightly awkward because it gives you something to do with the jacket off that maintains the formal register of the outfit. The key with a three piece is keeping everything else extremely clean. This isn’t the outfit for interesting accessories or experimental shirt choices. White shirt good tie clean pocket square and footwear that takes the occasion seriously. Let the suit be the thing because it’s already doing a lot.