The limit of a spell is force.
Force is tied to Magic for determining drain.
Initiation ranks add to drain resistance with a single metamagic quality.
Thus, initiation helps to resist drain, cast larger spells, and have a larger limits...
@Coyote,
Which brings us back around to dice pool and perceptions of dice pools.
There is a large and vocal community here that insists you need a dice pool of midteens to low twenties (14-22) to effective (or professional, useful, good, or whatever the descriptor of the week is....). Don't believe me, visit the character creation forums.
Seriously, someone's 'Average 17 Year old' has a logic higher then 90% of the people on the planet?

Come on! Every 17 year old I have ever met I have wanted to hit with a shovel -to hopefully BEAT some sense into them.... Ihat 17 year old, on a high school education is a better programmer then 70% of the 'professionals'

Perceptions.
Look, play the game however you want to play it, with whatever dice pool levels you want. IDGIAF.
But the level of contradictory whining by the same people, who usually haven't taken the time to learn or read all of the rules and history...... Just WOW.
So the Biggest agruments I have seen, boil down to 2 camps of basic thought.
Camp 1: there are too many skills, and because there are too many skills, I can build my super elite character at the aritrary dice pool minimums I have arbitrarily set.
Camp 2: skills don't reflect the vast range of knowledge that a person has, thus we need more skills and skill points so my character can have all these arbitrary skills, that may do nothing mechanically for the game, at an arbitrary value so I can be effective at the arbitrary skills that probably have no bearing on 90% of the game.
Well, Solution for both sides!
House rule it! The book tells you its a frame work, and a frame work only. If you don't like something you are free to change it! And you don't even need MY or the writers, or the editors permission! They have it to you in the introduction! (You did read that right?)
The only time what the book says matters verbatum is Missions play. And that isn't going to change (Heck, Missions play it can be argued is a dumbed down version of SR, what with banned qualities, racial meta types, and what not...)