When there are many attachments with the same filename, it is difficult for users to determine whether they are the same copy or which one is the latest version.
The Attachment Checker will alert the user that there is already another attachment with is able to block the upload if attachment has the same filename as existing attachments.
The user can then determine if someone has already uploaded the file or to rename the filename and re-upload again.the file.
...
Blocking of attachments with same filename can be enabled at Attachment Checker Configuration → Duplicate Blocking
...