Just quickly adressing this point: Sure, if I'm casting 'summon martini' I'm not going to overcast (unless I have a 30pt addiction to alcohol), but if I'm hiding behind a cargo container with lead buzzing overhead and grenades swiftly tearing through the available places to hide, I'd open with max overcasts and move from there. Sure, my hands will feel like they're on fire, and I'll have a migrane for a week, but at least I'm far more likely to come out of it alive and notably free of bullet holes.

There are reasons not to overcast, even in that situation: astral signatures, knowing you'll need to be at the top of your game for the next gunfight and so forth, but when your life is on the line, what's a little internal bleeding to you?

Apply the composition. Let loose the Agents. Cast the Clairvoyance spells. It's already gone noisy, let's rock and roll.

A goodly chunk of the time the Hacker doesn't need to be on-site, but the Mage almost always does, or is more seriously impaired if operating solely from the Astral Plane.