I'm interested to hear if any Loremaster has done that to their heroes and how it worked out narratively and mechanically.
I'm also looking to discuss situations that might qualify for such a impediment to the heroes. In effect it is sort of like turning the difficulty of the game to Hardcore mode

From the books three situations immediately spring to mind:
Frodo and Sam's time in Mordor would be a strong contender for such a ruling.
When the Fellowship attempts to cross the Misty Mountains and are caught in a snow storm.
When Thorin's Company are lost with no food in Mirkwood.
There are likely more.
As for other situations, the first couple I thought of were:
Being tortured (and then escaping/released etc)
In the aftermath of a particularly bloodthirsty battle
So feel free to throw out some ideas folks, either from the books or other situations you can think of. Or discuss what should and shouldn't qualify for such a harsh impediment. if nothing else it will be a good reference for evil Loremasters that want to be mean to there players, if we can explore it fully.