Archiving a design is always a better option than deleting a design.
Think of archiving as free online storage for designs you most likely no longer need.
When you archive a design, it means you can still order from that design, but you will not be able to make any changes to the layout once it is archived. Once a design is archived you cannot unarchive it - so double check your work before you decide to archive.
Lastly, archiving a design will free up an active design slot!