The most obvious that comes to mind is that automatic knives, often called switchblades ... Why add a whole separate knife to your EDC kit when you can add a second cartridge and have two knives ...

This doesn’t mean switchblades aren’t serious tools, though. Companies like Benchmade, CRKT, Kershaw, and Buck, all make automatic knives to the same standards as their other hardworking blades.

Weapons Universe Baltimore's ordinance defines a switchblade as "any knife with an automatic spring or other device for opening and/or closing the blade, commonly known as a switch-blade knife." ...