The low block is the tactical cousin of the high line: instead of compressing space high up, the team compresses space next to its own goal.
It suits teams that expect to be outplayed in possession. A 5-4-1 or 4-5-1 shape keeps distances between lines short, forces opponents wide, and creates fast transition opportunities when the ball is won.
Discipline is key. One midfielder breaking the line can open a passing lane straight through to goal.