The neck area is tricky, soft supple skin coupled with course hair and usually in a funny directions, mine is horizontal on one side.
If I do a downward pass everywhere, that means I'm going XTG on my neck area straight away and that is too severe.
If over tighten the skin to make it easier to shave that can also lead to ingrown's and irritation.
So for the first couple of passes genuinely go WTG until it low enough to go XTG, that means shaving from nose to ear and vica versa.
I try and keep all that neck and skin stretching to a minimum, you have to do it with straights but then you only need one or two passes.
I don't generally bother going ATG myself but if I do it will usually be on the fourth pass. IanM has also mentioned the difficulty in maintaining correct blade angle over contours and different directions, it's true it is difficult.
If you want a fairly fool proof ATG on neck, an adjustable on a low setting or very mild razor with a "sharp" blade should help. If you can't help going ATG because of the pattern of growth just take the greatest of care it's not worth the aggro for a few hours of smoothness, a couple of gentle passes will just have to do, after a week or two of a hopefully irritation free neck you might be able to pull another pass.
Alcohol also does it for me when it comes to calming irritation, I like the bite but it's not for everybody. When it stops biting I know I'm good but then I stink to high heaven.