Is it worth it? That is up for you to decide. Should a company require one? That, too, is up to you.
Personally, I have signed two: one at an excellent 135 company and the other at a less than desirable 121 company. In both cases, I fully expected to stay for the term, but was willing to repay the prorated amount had I been hired at Marvelous Mainline.
If you sign one, be willing to live up to it either by serving the time or paying what is owed. That is what an honorable person does. Not living up to the contract, IMHO, is as sleazy as many of our upper managers.