What are the advantages of going through the practice league? Aside from the practice and that battle.net can find better matches?
The practice league is usefull if you never played SC2 multiplayer. It uses
Novice maps where the entrances to both main bases are blocked by destructible rocks which prevent you from being rushed and shuts down many cheesy builds like cannon rush. Through this you have some more time to build up and get used to your buildings and units until you engage with your opponent.
Although when you get out of the practice league you maybe will have to readjust your play since there no longer is any early game protection.
IMO its better go do some custom games vs AI or people you know to get used to multiplayer and the maps.