there's something to debate. I don't use air or water cause I believe that the sudden change of temps will warp the metal. If I use air I will let it cool naturally for a little bit then zap it with air, but never right behind the weld.
My focus is more on what kind of area it is. Sometimes it can be surrounded by body lines and be tight/stout and I know I can somewhat hammer on the welds in those areas, then there's spots where you want to make sure it cools down to room temp after each tack. Just depends on the area.
here's an example.
I know I want my first weld on this job to be the one right in the door jamb corner, probably the most important tack of them all in terms of stopping any shifting while welding, other than a couple plug welds in the jamb to keep the gap. Anyhow, So I tack that side then the other and move on. I could have probably pushed it with 3 tacks but that's asking for trouble, but the thought crossed my mind cause I'm looking at the corners, which will contain warpage, and that horizontal body line(can't see in pic), which will also help in those regards.
Then you got this one
This one would appear to be a good one where you can get it a little hot due to the curve in it, but it's still a relatively open area and I'd much rather risk it
on the first area I showed rather than this area.