Why Do Sprint Burst Users Do That Thing

The thing where they wait until you're right up on them and THEN they start sprinting. It feels like it just wastes potential distance they could be making and I'm able to immediately catch up in a matter of a couple seconds. Wouldn't it be better to use it as soon as they notice me coming for them? I feel like I'm not understanding some kind of common strategy because I notice it constantly and it just feels like a bunch of players are wasting a perk slot.