Why maxFileSize and minFileSize are different from targetFileSize after optimization? What is the significance of targetFileSize? 

"numRemovedFiles": "2099",
"numRemovedBytes": "29658974681",
"p25FileSize": "29701688",
"numDeletionVectorsRemoved": "0",
"minFileSize": "19920357",
"numAddedFiles": "883",
"maxFileSize": "43475356",
"p75FileSize": "34394580",
"p50FileSize": "31978037",
"numAddedBytes": "28254074450"

targetFileSize: "33554432". Explain using the above information.