Welcome to FT. If the flight is oversold and there are not enough passengers to voluntarily (VDB) give up their seats then PAX will be involuntarily denied boarding (IDB). Though it rarely happens, one of the deciding factors can be check in time as well presence at the gate.

With Delta and other airlines they have a phone app that you can send your boarding pass to which also has flight updates. Using your phone also prevents the TSA from writing senseless squiggles - but then again they can record your info.

In the case of some airlines like Delta they give their medallion fliers a free drink coupon for checking in on line and printing their own boarding pass.

Mostly thought it saves the airline some time and money.