All options are available in both MP and SP. No cheating disables all modification tools (World Builder, Modded XML files in Root Folder, etc.) and debug tools. In MP, this is already done, as cheating is not allowed in any MP game ever. Therefore, the option serves no purpose. In SP, it serves two purposes, however:
1. A sort of anti-temptation lock. These are Start Game options that cannot be changed. I always turn it on as somethines the temptation is there.
2. For GOTM. Still, most of GOTM is "On Your Honor" anyway.
NOTE: This does not stop mods from working. It stops modified XML/Python/Other files in GlobalAssets from being used, and root if you have any there (Never Mod Your Root Folder, Ever!!!). IE: Say there is a mod that changes an icon for something. You like that icon, so you put your mod in the GlobalAssets folder, so all mods and main games use it. No Cheats turns it off.