Ah okay I think I see it now. I'm not trying to munchkin here in fact I'm asking so i understand the math one of my players is using to make sure it is correct. So let me see if I have this;
Sponsored Magic (-4) Gives Channeling and Rituals.
If one has Evocation or Thaumaturgy, but not both, then Sponsored Magic is (-3) for a total of (-6) cost.
With both Evocation and Thaumaturgy Sponsored Magic is (-2) for a total of (-8)? That's a LOT of expense but I guess it makes for a potent caster. On the other hand if you just take Sponsored Magic then you'd still be able to do spell casting but on a more limited but potentially more powerful basis.
Indeed, but you would not be able to specialize.
You'd be limited to focus items only to boost one's power.
The biggest benefits for sponsored magic in my opinion are
A. Flavor
B. Power. For 1 debt, a player can borrow 2 shifts of power from a sponsor
C. Fate point borrowing. RAW states that a PC can tag aspects without using a fatepoint at the cost of 1 sponsor debt.
The RAW are not clear on what exactly that means. I take it to mean that (and this is just my understanding)
1. If a PC gets above a certain amount of sponsor points (SPs), the patron can compel the character. I take this to mean that the sponsor can influence (compel) the character to act more like the sponsor. For instance, under the influence of /tons/ of hellfire casting, Harry started blowing things up whenever he got irritated - like outside Marcone's.
2. The more SPs a PC incurs, the more attention the PC gets from the sponsor. This can be either a good thing or a bad thing. When Harry was using Hellfire, he got angry a lot. When Harry started using soulfire all the time, he got visited by archangels more often and set on missions.
My biggest confusion is that the book does not make a direct correlation between fate points and sponsor points. The RAW is not clear on this issue at all... so I think it is GM discretion.
Sponsored magic is not the most powerful character build by far.
I personally like it and built a character on it mainly because I see so many stories being spawned from it and it gives an element of flavor to the magical system.
I personally don't see a whole lot of use for sponsored thaumaturgy at the speed of evocation. Maybe to make a quick circle or snap a quick tracking spell, but other than that I don't see how regular thaumaturgy is not as powerful or more powerful.