So, the thing is if you installed some other ROM but you did not liked it and want to revert back to your original ROM you can always restore your ROM only if you had backed up your ROM. Incase if your backed up ROM doesnot restore or you don't have a backup than you use flashtool to install the original version of your ROM. But there is one thing, your guarantee is already broken if you used flashtool or even if you install the other ROM and you don't have the original ROM that came up with your mobile.
Those files are just the original firmwares that developers have downloaded with PC companion and made the ftf file with Flashtool, so that it will be easy to install using flashtool.
So, if your mobile has the original ROM and you have not done anything then always update via your PC Companion or from Settings>>About Phone>>Software update.
For other people they cannot update from that method because they are not allowed due to many reasons and they need those ftf files from the link that you stated.
