It can be, depending on the design needs of a part. Since many designs call for plastic or resin materials, the designer may wish to known the limits of a material’s elongation. In general, elongation is the measure of how much strain a material can take before it deforms to the point of breaking or rupturing. Certain designs call for considerable elongation or the ability to absorb energy by deforming plastically. One example is a car bumper.
Most polymers, and some metals, register a high elongation compared to more brittle materials like ceramics, which do not deform. Rubber materials are an example of a high elongation.
This characteristic of a material is measured using tensile testing.
One can often predict the level of elongation if the tensile strength and tensile modulus are known.
Depending on the design, an engineer may want to know the elongation of a material “at yield,” which is the point the material deforms but does not break or deform permanently.