Due to collagen's structure, several tissues in the body, such as skin, are capable elastic deformation under a large amount of strain. It is designed for stretching -- how would we benefit from tendon or cartilage that could not regain its original shape after a strenuous event?
The amount of strain that a tissue with a collagen matrix can easily undergo depends on the amount and orientation of the collagen within the tissue. The protein's high amount of order on the secondary and tertiary levels contribute to its strength as well; in fact, collagen is stronger per unit weight than steel