Stratified sampling

Why stratified sampling performed at compression stage in tablet manufacturing or what is the importance of stratified sampling ???

Stratified sampling is the process of sampling dosage units at predefined intervals and collecting
representative samples from specifically targeted locations in the compression / filling operation
that have the greatest potential to yield extreme highs and lows in test results. These test results
are used to monitor the manufacturing process output that is most responsible for causing
finished product variability. The test results can be used to develop a single control procedure to
ensure adequate powder mix and uniform content in finished products.