Survivors who are affected with Status HUD/Haemorrhage are leaving blood pools behind them until healed. The Killer is notified when Survivors are bleeding by the displayed in-game Score Event.
Apt Killers can use the blood pools to track down an injured Survivor, which is especially useful if said Survivor has Iron Will and is otherwise silent. They can counter it if they heal themselves back to full health or use Template:IconLink
Visibility of the blood pools created by bleeding is not great. Without the Bloodhound Perk, they are almost invisible in grassy or dark areas.
Status HUD/Haemorrhage is related to the Status Effect Template:IconLink.
Combining the Perks Bloodhound and Sloppy Butcher will create an almost continuous red-line of blood on the floor, which makes tracking an injured Survivor a piece of cake.