The first white dress I owned was a cheap cotton shift from a market stall, and it taught me within one wear that white is never just white, it shows exactly what's underneath it, and I spent a whole afternoon at a colleague's leaving do angled against a wall so nobody clocked my underwear line.
Once I got past that lesson, the thing that actually matters with white is the shade and the finish, not the cut. True bright white reads crisp and a bit formal, good for a summer wedding or a leaving do where you want to look deliberate rather than dressed for the garden. Off white, the sort that leans slightly ivory or bone, is far more forgiving on the skin and far less likely to look clinical under office lighting, and it hides a faint coffee mark better than anything stark ever will. A linen or linen blend finish is the most practical of the lot because the texture does some of the work that colour can't, it stops the dress looking like a bedsheet and it creases in a way that looks intentional rather than slept in, which matters a great deal if you're wearing it to anything that runs past six in the evening. Avoid anything with a high shine in white unless you want every crease and every seam to announce itself under artificial light, because that fabric has no mercy.
White works harder in an ordinary wardrobe than people give it credit for. It sits well against tan or camel accessories through spring and summer, takes a denim jacket without any fuss on a cooler evening, and in autumn it can carry a dark blazer or a chunky cardigan rather than disappearing under it. It struggles in proper winter, not because of the cold but because white against grey skies and grey pavements can look a bit flat, so I'd keep it for the months when there's actual light to put behind it.
If you've got none, start with an off white midi in a slightly textured fabric rather than a stark white mini, it covers more occasions and forgives more mistakes.
Before I buy, I always ask myself one thing in the changing room, under the worst lighting the shop has got: if this fabric goes see through the second I step outside, am I actually prepared to deal with that today?