The section Size and Number of Data Files seems to apply for MMAPv1 storage engine exclusively. However, it isn't clear on the compact documentation page.

compact may increase the total size and number of your data files, especially when run for the first time. However, this will not increase the total collection storage space since storage size is the amount of data allocated within the database files, and not the size/number of the files on the file system.

WiredTiger doesn't use database files or multiple files per collection.

Thanks in advance!