If you have temporary access to VitaShell (perhaps via the H-Encore bootstrap or another temporary exploit) or are using a tool that mounts the Vita as a USB drive, you must place the workbin in the correct simulated PSP directory.
After installing a .vpk from the Workbin, you can delete the original .vpk file inside workbin to free up space. The installed game lives in ux0:/app/ or ux0:/game/ . Do not delete the installed app folder unless you want to uninstall the game. vita workbin install