This option allows you to choose how you would like to save your file in case of an existing file with the same name.
There are two different options:
Overwrite: The existing file will be replaced by the newly saved file.
Keep Both: The newly saved file will be saved with the same name as the existing file, but with a _1 suffix.
In case there are multiple files with the same name, the newly saved file will have a _2 suffix and so on.