In structural engineering, the typical Factor of Safety is 1.5. You take the intended load, and design it to 1.5 times. This is a fundamental load factor for analysis.
Along those lines, when you test to ultimate (ie failure) you can then determine the actual safety factor of each part or the assembly. In ultimate, you may determine a factor of safety of 5 for the part or assembly. This is what is strived for, because in the 1.5 factor being the bare minimum, if ultimate is only 2, then you are always looking at cases where the load or conditions may be higher than your assumption. With a higher factor of safety, you know you can cover more conditions without restrictions.