This tells the emulator to look for virtual hard drives and configs in your Data folder, not the C: drive.
: Your game progress, account logins, and custom keyboard mappings travel with the drive, eliminating the need to reconfigure settings on a new machine.
The trade-off is a slight performance hit (especially on USB 2.0) versus the freedom of zero installation and total data mobility.
You might be asking, "Why bother with a portable version?" Here are the top scenarios where Memu Portable outshines its installed cousin.