File with same file name in the same upload folder usually is the old file of the same field. When the record is updated, the files are also updated. (Other fields uploading file with the same file name to the same folder will get new file name index appended to the file name.)
Suppose a user has already saved a file and that file is used in other parts.
And some time later another user, without knowing the names of the previous files (which they don’t need to know), creates another file with the same name in another row…
The previous file of the first user is deleted. While it contained other information!