It depends what you're training for, what kind of shoes you wear to race and the overall volume and pace of the workout.
For example, I am primarily a road racer, 5k - marathon, currently training for a marathon. I have a lot of shoes, so here goes. I do easy/regular/long runs mostly in the Nike Zoom Elite, Nike Flyknit Lunar 3, Nike LunarTempo and Montrail FluidFlex. I do tempos and threshold workouts and longer intervals (1000m and above, fartleks, etc) in marathon flats such as the Nike Streak 5, Adidas Adios Boost and Mizuno Wave Ronin. For shorter intervals (800m and under), I wear the Nike Streak LT and Nike LunarSpider R5.
If you are a middle distance track racer (800m - 1500m), I'd recommend wearing spikes in track interval workouts. For 3000m and up, go with a 5k flat like the Streak LT for the majority of the workout, then switch to spikes for the last couple of repeats.