This is going to relate to electrical installations, as covered under the National Fire Protection Act. Looking at the back of a box of spade connectors you will see specific applications they can be used in, as well as a specific tool for putting them on. Any deviances from the manufactures applications and prodcedures results in violation of the NFPA and if you are doing work for the military, would be rejected.
A "legal" crimper is approved by the manufacturer of the spade lug, applies just the right amount of pressure, not too much, not too little.
Derek