Why use fastdl?

Fast DL --> Fast Download --> players are downloading the files on the server quicker and better.

I use FastDL and not the WSDL because the players coming on the server see the model, not ERROR

Many people come to rest, and not to look behind the loading screen =)

To speed up the incoming connection of players and avoid download errors from the workshop

on larger servers it might not have as much of an impact, but as far as i'm aware it works similarly to uTorrent's seeding in addition to compressing the addon files during downloads.

it helps players download everything they need during the loading screen so that they dont have to go and download the content files on their own

If a server does not use FastDL many players end up not wanting to join at all. You should consider having FastDL or WorkshopDL

FastDL is the best, and fastest way for your players to download server content. It is not easy to setup; one step wrong and your new players won't be able to join due download errors...
So, if you don't want to go over FastDL setup madness, "WorkshopDL" is your best option, it is still fast enough. I won't be explaining how that works tho, but it is way much easier, you can find tutorials on how to setup it up.

Just don't use "ServerDL" (engine's mechanism).

because it is faster, better and good, i would like to explain more but i dont speak very much english

Its when you join a server it download directly the addon of hin