And of course there are a lot of systems where that's no problem at all, either because the system is self-balancing or doesn't care about that kind of balance.
The only way such things worked well with games I've played in the past is where the GM was REALLY flexible, so much so that most of the tmie if you could come up with a story that was interesting and logical enough they'd let you have practically anything.
The last game I played with that GM I ended up becoming the Lord of Orthanc and commander of the goblin hordes below it. Wild game.
While the D&D community and the community of games built on it, like most of the d20 System games, consider balance to be paramount, a great deal of the RPG experience outside the D&D bubble just doesn't care.
If it doesn't do either of those things, your baby dragon is mechanically unimportant but it's still totally cool to have.
So that system automatically balances anything you have or can do because it always fits into the "help people/get in trouble" framework.
There's nothing about a baby dragon that is mechanically better than, say, being able to sing nicely or having an imaginary friend living in your thumb.
D&D and its ilk belong to a subset of RPGs with the general philosophy that you should figure out what stats a thing has independent of its impact on the storytelling. This is intended to create "realism" and be "impartial" (your mileage may vary), but it also imposes stringent limits on what you can do without disrupting the "balance."
I like how Pathfinder actually states in the GM manual that the characters can try to do anything. I try to impress that on my players. And usually even if it's outside the 'rules' I'll figure a way to make things happen for them. My main concern is personal, I am trying to impose a ruleset that I can lean on.
(In that question, someone is combining the "impartial realism" ethos with a "fiction first" ethos, which is fine--unless you care about balance.)
IE, he finds a scenario in which something is reasonable, then creates impartial rules for the thing, then discovers that the result-for-effort of the impartial rules are out of balance with the scenario.
"he finds a scenario in which something is reasonable, then creates impartial rules for the thing, then discovers that the result-for-effort of the impartial rules are out of balance with the scenario." - Such a short sentence, yet so many gems
This has been your whistle-stop tour of the contact zone between mechanics-first and fiction-first environments, in which I exerted a great deal of self-control in not mentioning the Fate engine.
