The three point line is shorter in the corners
Court markings
Why the arc is cut off at the sidelines, what that does to spacing, and why the corner is the tightest shot on the floor.
The three point line is an arc drawn from the centre of the basket, but it does not stay an arc all the way round. Near each sideline it straightens into two parallel lines running to the baseline, and those straight sections sit closer to the basket than the top of the arc does.
Under international rules the arc is 6.75 metres and the corner is 6.60 metres. In some professional formats the difference is larger, with an arc over seven metres and corners around 6.70. Either way, the corner shot is the shortest three on the floor by a noticeable margin, and shooting percentages from there reflect it.
The reason for the straight sections is geometry, not preference. A court has a fixed width, and a full radius arc at the same distance all the way round would run off the side of the floor before it reached the baseline. Cutting the arc gives a usable shooting position in the corner instead of a line that disappears under the scorer's table.
What follows from that is most of modern spacing. Teams station shooters in both corners because the shot is short, because the defender guarding it is the furthest from the paint of anyone, and because a pass from the top of the key to the corner is a straight line that is hard to intercept. A defender who leaves the corner to help on a drive has to recover a long way, and he has to do it along the baseline, which is the slowest path.
The cost is space. The corner shooter has the sideline behind his shoulder and the baseline at his feet, so there is no room to step back and none to drift. His feet must be inside a narrow strip and his landing has to be controlled, which is why corner specialists shoot with a fast, compact motion and catch with their feet already set rather than gathering into the shot.
There is one more detail that catches new viewers. The line is part of the two point area. A shooter whose toe touches it, even slightly, has taken a two, and officials check this on close calls. The same applies to a player who steps on the line while rising: what matters is where his feet were when he last touched the floor, not where he lands.