Why should I leave one or two "A used LULU Signature... " toy in my inventory when deleting them?

It's often advised that you can delete all the "A used LULU Signature..." toys, but to leave one or two in your inventory (including any you are wearing).

Why?

Because if your current HUD gets corrupted by the Second Life servers (happens from time to time), you can head to the Secret Warehouse , click the Update Switch, and start the update process to get a new set.

The update process requires you to wear the toy for the Switch to verify that you own one - and since the HUD is broken and you can't rez a new set, the only way is to wear any of the "Used" toys. It will detach immediately (used toys won't allow you to wear them), but the Update Switch would verify successfully, and you will get your new set.