Get your taxes done using TurboTax

This has always puzzled me.  Not the 6 digit IRS PIN and the confusion with the 5 digit TT PIN.  I've been doing that right for years.  My question is:  what is the TT PIN actually used for and when would one need it in the future?  Seems to me I just type in 5 random digits during submission and that is the end of it.