The "Magic Box" is what a local kid called my magneto when he couldn't think of what it was called . . . He stated, "My electronic junk is toast and I just want points again, or one of those magic box things." Here's the best way to explain magnetos for your application: from my own personal experience: Assuming your carburetor, engine timing and valves are correctly adjusted, set your magneto timing in the same manner as you would a common points & condenser system.
Harley 45 (WL), UL, ULH, K Models, Knuckleheads and Panheads: Magneto in solid "advanced position" at all times. It will cold start and hot start. I bolt my magneto solid in the "fully advanced position" and don't mess with it. The points last 5 times longer in a magneto than a conventional system. (don't ask me why, they just do) When you're cold kick starting, if the engine is poppin' through the carb periodically(not all the time) you're probably ok. You could barely retard your spark to help, but once it's running and hot, these engines like a little extra advance timing I've found for performance, mileage and "it just runs better."
Harley XLCH Ironheads and Shovelheads: You need the capability to retard (for cold starts) and advance (for running position) for best results. Kick starting a fully advanced magneto on an XLCH can be difficult with popping, kick backs, slips, and feeling the need to sell this thing . . .