On line permits with visual instructions

I have done a Copy & Paste and saved the instructions in my files. Could be useful at some point. But I still do not understand the reason for getting the permits ahead of time. We contacted the Mexican Consulate in Phoenix and learned you can go to any consulate to get your vehicle paperwork done ahead of time too. But we did not go because we were also told the only way to get our "migration" papers is at the border - but you can pay for them at any bank I think - not sure. So there is a stop at the border to do paperwork any way you look at it as far as I know. A couple weeks ago we stopped south of Nogales and went through the whole process and were in and out of there in just under an hour. We have had to wait longer - and we have had to wait less time. When we do our vehicle at the border we just hand them our paperwork and they fill everything out and have us sign and pay and that's about it. Getting the permit online may save some time but I am still not sure how. Can anyone explain this?