101.1 Whenever a card’s text directly contradicts these rules, the card takes precedence. The card overrides only the rule that applies to that specific situation. The only exception is that a player can concede the game at any time (see rule 104.3a).
I've never known what this rule is for.
As far as I know, Magic has rules that allow you to do some things and work together with whatever cards' effects are working now. Very few rules downright forbid you to do some things.
For example, there is no rule saying that I can't cast creatures anytime I could cast an instant, just a rule saying that I can anytime I could cast a sorcery. With Leyline of Anticipation, I now have two permissions. I can cast them anytime I could cast a sorcery and anytime I could cast an instant. So I'm fine and I can do the second.
But there are rules that forbid you to do some things, and here the cards have to get a little trickier. A creature with hexproof can't be targetted by opponents' spells and abilities. This is why Glaring Spotlight needs that ugly "as though they didn't have hexproof". Otherwise, there would be an effect saying I could target creatures with hexproof (redundant, since the rules already allow me to target any creature), and a rule saying I couldn't, and so I couldn't.
Another clearer example is the "you can't play lands except on your turn" rule. It's very difficult that a card bypasses this restriction. It would have to say something like "as though rule #whatever didn't exist", which is obviously unnaceptable text on a card.
My question is: Is there any case where 101.1 works? Is there any situation in which some card wouldn't work without it?