Final answer:
Mechanical fastening is preferred for its increased joint flexibility, beneficial in applications that require some level of movement, such as with flexible connectors in mechanical systems, and pinning which enhances mechanical strength.
Step-by-step explanation:
Mechanical fastening may be preferred due to a variety of reasons, but when it comes down to the options provided, the best answer is increased joint flexibility. Mechanical fastening systems, such as bolts, screws, and pins, allow for some movement or flexibility at the joint, which can be beneficial in certain applications. For instance, a flexible connector, like those used in various mechanical systems including bicycle brakes or hospital traction systems, can transmit forces effectively around corners while maintaining the tension direction parallel to the connector. Moreover, mechanical fastening methods such as pinning are known to increase the mechanical strength of a material by introducing defects that inhibit further material motion. This is in contrast to adhesive methods which may offer a more rigid solution but can fail to provide the necessary flexibility for certain mechanical applications.