A full-court press in basketball is a defensive strategy where players aggressively cover opposing players by spreading out across the full-length of the court with the goal of forcing a turnover. This can mean a zone defense such as a 2-2-1 or a 1-2-1-1 or a full court man-to-man, all are full court presses. The role of each defensive player varies on whether it is a zone or man but the goals always remain the same: to create turnovers, speed up the offense, change the momentum of the game, and take time off of the clock from the half-court offense.
Pressing in the full court with a deep team gives an extra advantage over a half court trap or press because it can cause the offensive team to tire more over time after to deal with pressure all over the court the entire game. This leads to more turnovers and steals as time goes on leading into the goal of creating turnovers and momentum shifts of the press. Besides shifting the momentum, it is one of the only ways in which a team can dictate the tempo of a game speeding it up or slowing it as they want depending on the amount of pressure that's applied. Shifting this along with creating turnovers along the way makes this a strong defense to use.
Although pressing can lead to great gains for a team, it can also cause many negative outcomes too. A good press takes a lot of moving parts to fit together nicely and if they don't it will lead to easy buckets for the offensive team. This amount of practice time used learning the press could leave a team behind in others facets of the game and in the end a press is a high risk high reward defense so even the best presses give up easy buckets from time to time. All in all, a full court press can pay dividends, although it is a calculated risk in the end that can go wrong too.