Why should we not always cut the edges of the nails really short? Because cutting doesn’t always change the forces acting on the nail. When the nail is cut off, depending on the shape of the cut, you change the nail’s shape in entirety. The faster- and slower-growing parts of the nail will keep growing at the same rates, so the change in the shape of the nail sometimes might get the nail to grow correctly or other times it might not.
The best cutting option seems to be to cut the nail in a rounded shape, such as an oval or to cut the edge so that it is slightly curved, rather than straight across at the end of the nail which would have a higher chance of digging into the toe. The rounded shape method seems to cause the nails grow at the same time outwards and not into the inside of the actual toe.
I’ve noticed that pregnant women and children tend to get ingrown toenails more often than others. That may be because typically nails and hair grow faster and more prominently in pregnant women and children.