The question I get asked most about petite dresses is whether "petite" just means shorter, and the honest answer is no, not if it's done properly. A proper petite cut shortens the bodice, moves the waist seam up, narrows the shoulders and often takes an inch or two out of the sleeve as well, so the whole dress sits where it should rather than the hem just getting hacked off a standard pattern. If you're under about five foot three and you've spent years taking things to a seamstress to fix the gaping neckline and the waist sitting somewhere near your hip, this is the fix, not a smaller size of the same dress.
Where it falls short is anywhere the dress needed drama from length, a big train hem, an exaggerated maxi, anything that wants fabric pooling on the floor because that's the whole point of it. Petite cuts aren't built for that kind of excess, and a floor sweeping dress taken up to fit a smaller frame usually loses the proportion that made it worth wearing in the first place. It also won't rescue a dress that was badly drafted to begin with, shortening a bad shape just gives you a smaller bad shape. What tells you a petite dress is properly made is the same as any dress really, a fabric with enough weight to hang rather than cling, seams that sit flat at the waist instead of puckering, and a hem that's been finished as its own thing rather than just turned up twice and pressed. Cheap petite ranges often skimp on the lining, so you get a dress that looks fine on the model and clings in all the wrong places by lunchtime. Check the lining goes the full length, not just to the knee.
A petite dress clashes badly with anything oversized layered on top, a big slouchy cardigan or an oversized blazer will swallow the proportion you just paid for, so keep the outer layers closer to the body, a fitted jacket or a cropped coat does the job without undoing the cut. Heavy boots in winter can also throw the balance off if the dress is already short in the leg, a slim boot or a low heel keeps the line going rather than cutting it short twice. For spring and summer a petite dress in a lighter fabric earns its keep on days when a full length dress would feel like wading through fabric, and for autumn, a good petite shift under a fitted coat is about as practical as dressing gets. Next time you're trying one on, check the waist seam first, if it sits at your actual waist rather than somewhere near your ribs or your hips, the rest of the fit usually follows.