"Save As" creates a new, separate copy of your current document while keeping the original file intact. You should use it primarily when you want to preserve the existing file unchanged and start working on a modified variant under a different name or location. This differs from simply clicking "Save", which overwrites and updates the existing file with your latest changes.

Use "Save As" when creating versions, like saving a report draft as "Report_v2.docx" after making significant edits while keeping the original "Report_v1.docx" for reference. It's also essential for saving a file in a different format, such as exporting a Photoshop ".psd" design as a ".jpg" image for web use or saving a Word document as a PDF. This function is standard in virtually all applications handling files, from Microsoft Office to graphic design software.

The primary advantage is preserving the integrity of your original file, preventing accidental overwrites and allowing version history. However, overuse can create clutter with numerous similar files requiring manual management. Always using "Save As" responsibly helps maintain organized workflows and ensures you don't lose important work.