Scanning in football is done to locate teammates, opponents and the space around them, so players can get a full "picture" of their surroundings.
The ability to inform yourself to what is around you all the time is an essential quality and habit.
Without this essential skill (scanning), a player is unlikely to make consistently good decisions and consequently will lead to poor positioning and ineffective game actions.
Scanning in football is fundamental to performance but is too often overlooked.

Scanning football - Some opinions from the world's great coaches.
"Making the right decision at the right time is the hardest thing in football" Pep Guardiola."Think fast, look for spaces. That's what I do: I look for spaces. All day long. I'm always looking. All the time, all the time" Xavi Hernandez.
"The difference between the players is the ability to assimilate information.
In the Premier League, good players take in 4 to 6 times before 10 seconds before they get the ball and the best players take in 8 to 10 pieces of information.
It is therefore important to use exercises that help to increase this ability to gather information. "Arsene Wenger.