[Bradd]

You can drop things as a free action. You can drop sustained spells as a free action. Can you do more than one at a time, for a single free action? For example, can you drop everything in both hands? Dismiss all of your spells at once?

[anotherJack]

Yes for the objects, it's in the core ruelbook. Fo sustained spells, the core rulebook RAW says you can drop one spell with a simple action.
I think I would allow to drop all your sustained spells, but it's not RAW.

[Walks Through Walls]

Part of that might come from even the best of mages will have trouble sustaining more than 2 spells and doing much of anything else.

-6 dice pool penalty for keeping 3 spells going limits things quickly

So they may not have thought about have several spells to drop at once and wanted to be clear about you didn't have to drop all your spells at once

[anotherJack]

And since the sustaining penalty semmes to apply to resistance test, yes a mage may not want to sustain too much spells.
But how about sustaining foci and spirits ? do you have to deactivate the focus to stop sustaining the spell, or can you stop the sustaining with an autoamtic action without deactivating the focus ?

[Walks Through Walls]

With the spirit it would have to be a command to the spirit to stop sustaining the spell so that is a simple action I believe.

For the sustaining focus once you make it sustain the spell it is no longer the mage sustaining it so I would say you would have to deactivate the focus to stop the spell from continuing.