Currently trying to get my 10km time down running 40 mpw and here's my perspective:

general performance: I love the idea that if I pick up a random sport to play with friends or am in some emergency situation I know I can move faster

personal achievement: it feels great to break a new personal best

time constraints: I can hit my distance goals with less time spent during training if I'm moving faster, I only have about an hour to run on week days and getting more miles into that time is helpful