The old files are no longer needed because you have an extra backup of the files.The mail and attachments that are useless are still stored in the drive in the Trash.There are so many redundant files on the drive taking up a lot of space.The storage space is running out and you need some space to backup new and important files.There are various reasons why the users would like to empty Google Drive trash.
How to Recover Deleted Files from Google Drive Trash Fix 'Google Drive Empty Trash Not Working' How to Delete Files and Empty Trash in Google Drive