Why are we doing jump squats, lunge jumps and other plyometric drills at speed sessions?
Researches studying running science (e.g. Paavolainen et al at KIHU Research Institute for Olympic Sports in Finland) have shown that runners can improve their speed through plyometric training, even if it replaces an endurance run once per week.
In lay terms, explosive drills teach your nerves and muscles to fire more quickly. This will increase the rate of your stride purely by increasing the power of each push off. This makes you faster for each stride you take without increasing your stride length. Pretty powerful stuff!