Why disconnect the negative

[Lakota 5,000+ posts]

From a safety standpoint there is a big difference which wire you remove first. If you take your wrench to the positive terminal and accidentally touch it to a metal part you can accidentally cause a massive short circuit complete with sparks, molten metal flying through the air, and possibly an exploding battery. (assuming a negative ground vehicle)
If you had removed the ground wire first there would be no short circuit if you accidentally touch your wrench to a metal part of the vehicle.

Pretty much what I was trying to get at, but your explanation makes more sense.