The 7z format is popular because it often performs better than standard ZIP files:
Often, large files are split into smaller pieces to meet email or upload limits. In a "spanned" archive, you might see files like archive.7z.001 , but some systems use custom naming like AL01.7z for the first volume.
It can handle incredibly large files, theoretically up to 16 billion GB.
It could simply be a specific filename given by the creator (like "Archive List 01"). Key Features of the 7z Format