HEPA makes sense if you filter all the air, ie. the filter is inline like in a laminar flow cabinet/cleanroom or directly inserted in an air stream filtering 10

HEPA makes sense if you filter all the air, ie. the filter is inline like in a laminar flow cabinet/cleanroom or directly inserted in an air stream filtering 100% of the downstream air. In those cases you care a lot about how many particles make it through since they will cause yield loss or contamination in the processes.