The game mechanics that are important: "Whatever the ambient mana conditions are, the character always stands at the heart of a Rating 4 background count (see p. 117, Street Magic) that extends a number of meters from her body equal to her Essence; this background count also impairs her own actions if the character is Awakened."
While you might think that it's neat that those wards you're trying to sneak through are weakened by 4, mind that you will forever have a -4 to all Assensing tests, and any wards you try to create and spirits you try to summon are doubly impacted by your haze. Assuming Magic & Essence 6 (typical starting magician) with Astral hazing, your effective Magic is really 2 and the maximum Force spirit you can summon is 4, which is then immediately Force 0 and gone; the same is applied to wards you try to create. Any and all bonded foci you have are also equally weakened, so you're paying karma for 4 levels of power that you'll be hard pressed to use until you've initiated twice to learn the Cleansing & Filtering techniques, and that's assuming you've managed to get a hold of anything that's at least Force 5 and greater. Your magical friends will also likely loath to be close by you, as they will also see a -4 to everything magical they have. And don't forget that Adepts within your haze will lose at least 4 Power Points of abilities (accounting for lost discounts on selected Way powers).
And at GM discretion, if you're sitting around in one area for too long you'll start leaving your taint behind (from the "similar" cyberzombie rules, Augmentation 157-158, no choice, the aura will expand by 1 meter every 2 to 3 hours, which dissipates at a rate of 1 point per day). You will leave behind an astral trail that will not be too difficult to follow (the Astral Chameleon quality will not improve this), and your home will be forever tainted (and the warding of your lodge forever reduced) unless Cleansing is an option. You'll also likely lose some magical friends if you ever become infected with FAB III (Street Magic, 127), which will forever hang around you as a Force 4 plague if you cannot convince someone to cast a Sterilize or Cure Disease spell or you can actually beat it up in astral combat (if you cannot do any of these yourself).
