Ballet pumps are the shoe you reach for when you want to look like you made an effort without your feet knowing about it, and that's exactly why they're worth having. A proper pair, with some structure in the sole and a bit of padding under the ball of the foot, gets you through a full day of walking in a way that strappy sandals or anything with a heel simply won't. The whole point is that they disappear on your feet.
They're not the right choice for distance, though, and I mean that literally. Anything in soft leather or, worse, a thin faux leather with no real insole will start to feel like cardboard by the time you've walked forty minutes, and your heel will have slipped and rubbed somewhere around the twenty minute mark. They're also not built for rain. Suede ones are a write off the second a puddle looks at them, and the kind with a leather sole go slick on wet pavement almost instantly, so they're a poor pick for a proper British fetch the kids January rather than a mild September.
Where they come into their own is anything that needs you upright and presentable for hours without being formal about it. A long lunch, a gallery, a work thing where you're on your feet greeting people, a spring or early autumn day when it's not quite boot weather but trainers feel wrong. They sit well under cropped trousers and midi skirts especially, because the cut off at the ankle is doing something flattering that a trainer just can't. What they don't sit well under is anything heavily tailored and formal, like a sharp suit, where they can read a bit too flat and casual against structured fabric, and they look odd with anything that has a lot of volume at the ankle, like wide cropped flares, because the shoe gets swallowed.
Fit is where most people go wrong, and I include myself, having bought a pair half a size up once thinking ballet pumps "run small" as a rule, which they don't, consistently. They should feel snug on the first wear, almost too snug, because leather and suede both give a little with wear and will loosen within a couple of weeks. Buy to the shape of your foot rather than a stated size, since a square toe box and a pointed one fit completely differently even in the same size label. Watch the back seam too, as a pair with a shallow heel cup will slip at the back no matter how well the front fits, and that's the fit problem that ruins an otherwise good pair.