With an automatic valve body, launching in any gear but "1" places all of the strain on the overrunning clutch (sprag) which is a known weak link in the TF, that's why it's not recommended. In "1" the rear band is applied and takes some of the strain off of the sprag. Of course, any second now someone will pop up and declare "I been launchin' in 2nd for xx years and never had a probem". I can only advise.

The best setup is a billet rear servo piston and heavy return spring/retainer, there will still be some overlap on the 1-2 upshift but not nearly as much as with the factory parts.