Touch passes are thrown when the only way to get the ball to a wide receiver is through a tight window. In most cases the gap is in front of the safeties but behind the linebackers. That type of pass must fall within the tiny area or it could be intercepted.
A quarterback with the ability to throw an accurate touch pass poses a large threat for the defense. The defense is less likely to call a zone because of the pockets of space it creates. By eliminating a coverage scheme the offense then has a better guess of how the defense is going to defend them.
It is important to note that a touch pass would be ineffective if thrown on a tight line without loft. To generate loft the ball must be tossed with finesse with more of a focus on the aim than the speed of the pass. When throwing a touch pass quarterbacks try to deliver the ball to the receiver as soft as possible.
Instead of fully following through the quarterback will stop after releasing the ball as well as not bringing their arm forward as fast. This way the speed is taken off the ball and it can be fitted into the window it needs to be.
A touch pass in football can also refer to a play where the quarterback snaps the ball and then quickly shovels it forward to a wide receiver in motion. The exchange happens so quickly the quarterback appears to have just touched the ball rather than fully gathered it.