just to clarify/provide an example why someone might want to use fling instead of levitate, i'll provide the following:
a mage wants to throw a knife at someone, and has both the fling and levitate spells.
if he flings the knife, he has a threshold of 0 for the spell, and a limit of <force> hits. the knife deals damage based on magic attribute, not on spell force, so low-moderate force is not a huge limiter really.
if he levitates the knife, he has a threshold of 1 for the spell (must achieve 1 net hit to lift the object) meaning he has a maximum number of net hits equal to <force - 1>. he has no defined strength damage, and it may take him multiple initiative passes to guide the knife to the target (note that fling requires 1 IP, whereas levitate moves objects on a per turn basis). furthermore, because he is likely to need to sustain the spell, he probably takes a -2 penalty on most rolls during the time he is making an attack. additionally, note that levitate has a movement rate determined by net hits (ie hits beyond the initial threshold of 1/200 kg), not just hits.
so then, for the purposes of throwing stuff at people, levitate probably takes longer, has a lower number of useful hits, requires that you sustain the spell most likely, and has a shorter range, given 1 IP to hit. it also does not define what the strength of the spell is, and i personally would rule that it is either lower than fling or at best based on force, rather than magic. on the other hand it can also be used over multiple rounds, can be placed into a sustaining focus, and the spell has more other uses.
fling deals a specified amount of damage based on magic (not force), gets the object to the target instantly, doesn't require sustaining, and has a higher number of possible hits. on the other hand, it's pretty much only good for one thing...
now of course, if we're talking about, say, throwing a garbage dumpster full of paper at someone, then levitate has the advantage though

[edit] oh, and sorcery 10 (assuming you mean spellcasting 10) can be achieved. it requires a spirit or other critter, though. so if we change the situation to a magician who conjures a force 10 spirit of man, we end up with a fairly similar situation. [/edit]