Part of the fun of street football is the aesthetic. To unlock the best shirts, shoes, and accessories for your created player, you usually have to win tournaments. If you are reinstalling the game or playing on a new device (like an Android phone or a PC), you likely don't want to grind for hours just to wear your favorite virtual boots. A save file transfers all that progress instantly.
Once you've installed the save data, take your emulation to the next level: fifa street 2 ppsspp save data
There are two philosophies here: