Historically, spring operated catch (or trap) points were installed on double track lines to derail runaway trains.
When a train passed over the points in the right direction, the points would move into line to allow safe passage, but if a train was travelling in the wrong direction, it would be derailed. Reduced freight traffic and reversible working on double track lines have resulted in the removal of catch points that fulfilled this role.
Their other use allows a train on a branch line to approach a junction and stop immediately before it, even when another train is running along the mainline as if the branch line train fails to stop, it will derail at the catch points, rather than foul the mainline. This facilitates the more efficient use of track at junctions and allows trains to operate more efficiently.