MechaPilot
Explorer
Well, we discussed about that. I think it's, in the end, a false promisse.
Long story short: in many occasions, if the DM has to impose restrictions, s/he is the bad guy, spoiling the player's fun. If s/he takes out restrictions, s/he is the cool guy; the one that "breaks" the rules so you can "have fun".
Doing such changes (imposing restrictions) between long time friends is easy - you can do almost anything in this case. But with some people you met not long ago, and have the "everything goes" mode activated, this can have serious impacts. You may even lose players.
I even admit it took a while for me to appreciate limits like this. I wish I don't have to convince all new players of that before they begin playing at my games; that's a lot of energy hahaha.
I disagree that it's a false promise.
My most recent group did not consist of long-time friends when it came together. However, they have accepted my ban on long-range teleportation magic, my ban on multiclassing without appropriate in-game justification for it (even if it's just something from the character's history or background), my ban on halflings, my refusal to hand out +X magic items, etc.