What are meta-currencies in games? Resources the characters don't know about that are being tracked and used by the player to "buy" things for the character. Fate points. Drama points. Bennies. Inspiration. Momentum. Devil's Luck. There are many names for these things. They are all awful.
Why? Because, as I've already said, their existence is entirely outside of the game world, and not representative of anything within the game world in any tangible way. I'm considering a term for these sort of mechanics beyond simple meta-currency. Storygamer trash mechanics? They exist, kind of like die pools, to hide the obvious shortcoming of the system involved by making up for said system with an easy "I win" button standing outside of said system. This above and beyond systemic pull toward success (the weakness/failure/cancer of die pools and those who enjoy them) so that even if said system causes a failure on the part of the character's actions, it can be averted by tossing a chip into a bowl or eating a pretzel or whatever.
This is all in lieu of designing a mathematically sound system and playtesting that system to where it is even more mathematically sound. You can't argue that this isn't the case, it's literally working like it should; I'm merely restating the mission statement of meta-currencies by stressing the negative element identified within all of them.
Take a game like Mork Borg with it's 6 system elements (stat rolls, DR for actions, reduction for armor, morale, initiative, and whatever stupid bullshit half-mechanic your 'optional' class staples on), the meta-currency in that system exists to make up for the fact that there really isn't a system in place. Meta-currencies pair with minimalist trash just like seeing rat feces on your entree, right next to a big cockroach.
There are a few good games where meta-currencies don't immediately detract form the entire game, usually because the meta-currency in question is extremely simple and doesn't have multiple options for a player to mull over. Also they are exceedingly limited in nature, not intending to become an economy within the game system. Simpler is better when it comes to meta-currencies. Why does MB have 6 systems and 5 uses for fucking meta-currency? Because it's heavy on the trash and light on everything else. I'm not going to say this lightly: if you like MB you might actually have some form of mental impairment. Seek help. In an entire industry of games for 10-12-year-olds, it's a game for a toddler. And one that's not overly bright.