The sensor has an air gap and the teeth of the flywheel are slightly different height between them and the gap, I'm presuming that where it tells you to set the tdc should see you just off the peak of the tooth on the flywheel and that means when you install a new sensor then it will allow a more reliable gap.
That or it will stop a fault code being generated or the ignition cycle being correct and not upsetting the fuel injected/flooding.
All of the above though sounds like a bollox reason to be a problem.
Personally I think it isn't a problem if you are careful, i usually gently offer the sensor into the hole while I manually slowly crank the crank pulley around and I can feel the teeth scraping on the sensor then I feel for the tooth at it'd highest then I lock the sensor in and then it's done.
That's just my thoughts though.
You could always just do what it says and rest easy though
56 350 2.2 130ps mk7 with 2 side doors
65 290 2.2 125ps custom with 2 side doors
07 350 170ps
Ids v86 licence + v86.04 update + xprog
hereIds map
here