I’ve had a few such questions over the past few months, so let’s try and cover all the bases at once.
I always wear “metal tabs” (side adjusters, side straps, strap and buckle) with my suits and similarly formal odd trousers. And I prefer belt loops with my casual trousers (chinos, jeans, cords).
With formal trousers, belts and therefore belt loops should be avoided for several reasons. They detract from the formality of the suit; they interrupt its clean, well-tailored lines; they are uncomfortable on thinner, worsted cloths (would you wear a belt with pyjamas?) and when cinched tight, they buckle the trouser waist, creating an ugly bunching.
So no belt loops. Why not tabs with buttons? Because they tighten elastic inside the waistband all the way around the back, creating similar bunching. At their tightest, the look is not that far off the elasticated waist of tracksuit bottoms. Side tabs, even when highly cinched, restrict any bunching to a couple of inches on either side. Plus they offer a continuous range of settings – buttons are discrete.
And why not braces? Well, I can see their virtues and I’ve tried them consistently on one suit, but they are not for me. Yes, the line of the trouser is cleaner and no shirting is exposed below the jacket’s waist button. But I spend some time every day in just trousers, and the high rise then looks unstylish and frankly unflattering. I also find the comfort of greater room in the waist is outweighed by the discomfort of having barathea wrapped around my shoulders.
By the way, side straps should be positioned on the waistband seam, not the waistband itself. This makes them more comfortable and, if worn at the hips as I do, adds an extra inch to the rise. The waistband is amply hidden when wearing a waistcoat.
I enthusiastically recommend side straps, particularly if you currently have belt loops on your suit trousers. Belt loops can easily be removed by a tailor, and side straps can be made out of the turn-up on the inside of the trouser leg, if enough excess has been left.
And then why belt loops on casual trousers? Because side straps don’t work as well on very heavy cloths, and their weight makes slippage less of an issue. Plus, I like belts. They are another opportunity to wear beautiful, hand-stitched leather and to accessorise effectively. A good belt can add colour in a way that would be garish in leather anywhere else.