What effect does the team intensity have during a game?

Just a match, because i know that if turned up during training, the players work harder, but is this the gas during a match?

The intensity setting is for the Training only, not match. :D

Increased intensity during training, means more skill points. But increased frequency of training is better.
More skill points earned from training and match play means increased quality.
Increased quality per player means improved team and squad overall quality and increased market value.

Whether they play better......is debatable... But it should be, cos how else do you improve performance?

You have to fined a fine line when heavy training, too much will bring you a lot of injuries.