[marfish]

I can't find anyway mentions it...

[MercilessMing]

No.  I don't have a page reference, but they do not need constant LOS for the act of sustaining and that's been consistent throughout SR.
When you want to move an AOE I think you do though. 

[Odsh]

And it's kind of strange that they never added at least a range limitation.
A.f.a.i.k. a sustaining focus is worn by the caster, so you could with one continuously maintain a spell from the other end of the world.

[Odsh]

And it's kind of strange that they never added at least a range limitation (or did they in 6ed maybe?).
A.f.a.i.k. a sustaining focus is worn by the caster, so you could with one continuously maintain a spell from the other end of the world.

[Reaver]

Ming is correct.

At the time of casting, line of sight to the target is needed. Once the spell is cast and sustained, Line of sight to the target is no longer needed. HOWEVER, to move a area effect sustained spell (like Chaotic world, or Orgasm) The mage must be able to see the area that the spell is to move through AND to.


At Odsh:

Even with a sustaining Foci, there is an upper limit to how long a mage can sustain a spell. Which is the limit of his endurance, once he can't concentrate, the spell stops.
(AKA when he goes to sleep) so really, the upper limit to a sustained spell is 2 to 3 DAYS. After which the human mind is such a mess it can't maintain concentration.


****

(And don't even THINK about trying to say "well he can just concentrate while he sleeps!" It never ends well when people try that logic fallacy) 

[Shinobi Killfist]

I think what throws people on this is the levitate spell which added a bizarre unneeded extra limitation on it, especially on top of the fairly large weight change.  But it states if you lose line of sight the spell drops. Maybe a errata fixed it, but as it is never explained anywhere it makes you wonder if that is the exception or the rule.

[Xenon]

Levitate is not actually ending if you lose line of sight (and was also not in previous edition), you just can't lift and move the subject while you don't have line of sight (at which point gravity will take over). If you establish line of sight then you can keep levitating the subject (without casting the spell again).