I assume you are referring to this guide → Tutorial: 2020 North America 2.20 Map Installation (Stand-Alone without Reformat) with Updated NAV_Voice 06/21/2021
As it’s stated there, that guide is targeted to MY20/+ units that CAN’T be reformatted.
As a general recommendation we always say reformat is the way to go, since it’s a cleaner, easier and faster way of upgrading a unit.
Of course you can use that guide for older hardware as well, general procedure is the same. But since older HW can in fact be reformatted, it’s up to the user which method to use.
Again, you are not mentioning which Sync3 version you are running at the moment, but latest builds had many bugs fixed.