If you attempt to use a command block in single player it will not save what you tell it to do and say "You need to be in Creative mod and oped to use command blocks."
MC-4810
Command Blocks In Single Player
Resolved
Works As Intended
1
Well if you create adventure maps or something similar you don't want your players to modify your command blocks, do you?
Tho that "you need to be opped" part could be removed from plain singleplayer as you are already some kind of op (if not in LAN)