For most healthy adults, a pinch of salt in morning water does not hydrate the body better than plain water, and several of the claims behind the trend go further than the evidence supports.
The one clear case where it helps is when someone has already lost a meaningful amount of fluid and sodium, through heavy sweating, a stomach bug, or a long fasting window.
Outside of that, the practice is mostly neutral, and in large enough amounts it can push daily sodium past recommended limits.