Minecraft wiki entry for Debug_mode, associated text: The set biome for this mode is plains by default in the Overworld.
The sun is displayed as if it were the beginning of the day (time 1000), but the daylight cycle is disabled.
Regardless, the time can still be adjusted with the use of the /time command, and the daylight cycle can be toggled with the use of the /gamerule doDaylightCycle command. The time can be also advanced from nighttime to sunrise with the use of a bed.
Using a map does not create an accurate map of the blocks in the world.
This type of world is the only type where barriers spawn naturally.
After setting the world type to Debug Mode, the Game Mode button is locked in Spectator, and a line of text appears beneath: "You can look but don't touch".
There is, however, nothing preventing you from changing the game mode using commands, as long as you have cheats enabled.