Do stringers use ATW or no? And would it be ok to request such a service, or is it something not taken pleasantly?
An ATW is used on certain racquets that require top down stringing of the cross strings and you want to have the stringing job done as one piece and the main strings end at the bottom, in otherwords where the main strings end at the bottom, and you want to start your crosses at the top because of certain manuf. require stringing patterns with top down stringing of cross strings,(I string most all racquets top down as that places less stress on the racquet than stringing bottom up) an ATW pattern is then required to accomplish this when the main strings end at the bottom or throat of the racquet.
If you string 2 piece then you can easily accomplish this top down with no problem.
Some racquet manuf. like Head requires 2 piece stringing of all of their preformance racquets with no one piece with an ATW, as they said would void their warranty. Many do string Head racquets with an ATW with no problems at all, but I wanted you to know this if you do request this on a Head racquet you take the responsibility if something goes wrong.
Watch a video of an ATW like this one below, and you will then understand more. YULitle does a good job of explaining this concept, and why.
http://www.youtube.com/watch?v=E-LEiTpNrnk&fmt=18
Also go here and you can see a good # of videos on stringing that should ans. most of your questions.
http://tt.tennis-warehouse.com/showthread.php?t=172626
Although I string a few racquets with an ATW every so often, just to keep in practice of doing them, as there are a few ATW patterns out there.
The bulk of my stringing is 2 piece due to the following:
All the hybrid stringing(hybrids can only be dome as 2 piece).
The Head requirement of 2 piece on their preformance racquets.(Yonex and Prince lists a # of their racquets to be strung 2 piece as well).
I prefer to string nat. gut as 2 piece, as less wear on the string that way.
I have yet to have a client specify 1 or 2 piece stringing, as most have no idea on stringing at all anyways.