Once the Gray Man appears 20+ times, he becomes omnipresent. He will stand in doorways, block paths, and instantly end dreams. This is a famous soft-lock. The save editor is the only way to globally reset his counter without deleting your entire 60-hour save file.
This is the #1 use case. You’ve played for 15 hours. Your Dream Index is stuck at 47%. You’ve seen Bright Moon Cottage 500 times and the UFO dreams zero times. The editor allows you to peek under the hood, see that your Static Bar is at 0xFF (corrupted), and fix it without restarting. lsd save editor