Compared to most other alcoholic beverages, beer is unique because it is unstable in the final package. From the day it is bottled, the quality starts to decrease.
The rate of decrease depends on time, temperature, and batch variability. The most important for consumers is colloidal stability of beer during storage.
Most customers are not willing to accept a glass of beer which is hazy. Due to the fact brewers must be sure that beer is stable during its shelf life.