Every race is a search for your individual limits. In an interval workout, the coach tells you exactly how many repetitions to do, and then you stop. The limit is imposed externally. 

Disruption and a skewing of your personal space is a way to challenge your comfort zone and grow towards becoming a seasoned athlete who can perform in unfamiliar territory.

Similar to disrupting the number of reps, or timing, we can skew the planning of the workout structure, allowing individual athletes to fine-tune it according to their own preference and stamina.