One player sleep changes the night-skip rule so the server can move to morning when just one person gets into a bed. You still have the normal day-night rhythm, but you lose the usual standoff where builders, miners, and AFK players get dragged into a server-wide bedtime debate.
The big difference is pacing. Night stops being an interruption everyone has to solve together and becomes a quick, practical choice someone can make when it helps: clearing a thunderstorm, making surface travel safer, or just getting back to daylight without waiting on the whole player list.
On survival servers it also shifts coordination in a good way. People underground can keep strip-mining, farms can keep running, and the player on the surface can skip a rough night without turning it into a vote. Most servers add a short countdown or cooldown so it stays convenient without one person constantly flipping time on everyone.
It is a small rule change, but it tells you what the server values: shared time and uninterrupted play.
