Hard mode sounds like the honourable way to play, but it changes the maths of the game more than most people expect.
What hard mode changes
Once you reveal a green or yellow letter, every later guess must use it. You lose the option of a throwaway probe that tests five brand-new letters.
The trade-off: more discipline, less flexibility when two or three answers remain.
Who should turn it on
If you already solve in four or fewer, hard mode is a fun constraint. If you lean on wide probing guesses to escape tricky endings, it can nudge your average the wrong way.