Why do biologist measure the number of trophic levels in an ecosystem?

Answer;
Biologists measure the number of trophic levels in an ecosystem so as to check its stability and health.

Explanation;
Trophic levels are the feeding position in a food chain such as primary producers, consumers, etc. They are positions that an organisms occupies in a food chain (series of steps in which organisms transfer energy by eating or being eaten);- what it eats and what eats it. 
Theoretically there is no any limit to the number of trophic levels in a food chain or number of organisms that live on each level.