For me, save restriction does not work in hardcore stealth games because there is no alternative.
If I fail this knockout or get accidentally caught here, then I have options:
quickload
die and replay a whole section from scratch
run away and wait for a long time, after which have much more problems during the whole rest of the mission because every guard is prepared for combat (and killing people is annoying and often forbidden)
That's boring!
The options 2 and 3 are absolutely opposite to having fun!
What is even worse, if I start to care about risk, then I have to restrain myself from exploration. I should not go to some places because I find them too risky! Doing so is absolutely stupid in a game like thief/TDM, where exploration is the core aspect of the game.
I never understood what's the pleasure of playing TDM/Thief in ironman mode, even though I tried to do that on a small mission.
On the other hand, I won Dishonored 2 in ironman mode without dying/loading and had a lot of fun with it. And the reason why it was fun is that I knew I had a lot of alternatives when I messed up. Like sleeping darts, stun weapons, and unarmed combat. And most importantly, I could pull out my pistol and shoot out through the crowd if things went really bad! As the result, the cases where I failed stealth were the best moments in the whole playthrough, even though I was mostly stealthy and non-lethal.
No-killing is a tradition for TDM, we cannot go against it, partly because AI is tuned to calm behavior more than to combat.
Turning the player into fighting beast (like in Dishonored) is not an option either.
Hence there is no way to restrict save/load without breaking the fun completely for most players.
And speaking about cheats in general, there are many reasons to have them.
The most important is young players (although this probably does not apply to TDM) and players lacking skill.
My dad was a geek. He brought PC to our house when I was six, and showed be QBasic. He also showed me how to use Hex Editor to change gold/time in savegames before anything like Artmoney existed (that was DOS times, so I converted between hex and decimal on paper).
I remember how I lifted time restrictions from games, like Prince of Persia and King's Bounty. That's the only way I could play through those games at that age. Of course, much later I revisited them and won them without cheating.
I played ADOM for a long time with backing up my savefiles, effectively removing the permadeath restriction of roguelike genre. The fun thing: it did not help me to win the game After spoiling myself with reading a lot of wiki, I managed to win the game and then started to play it without backups.
On the other hand, I'm opposed to having such customizations anywhere in the menu. Having more options usually means that things break more often, and also it hinders players away from the experience prepared by the mapper.