Okay, I am an engineer and I teach one of the PMP classes as night school at the local college.
For engineers, I do not think it is necessary (I don't have it) -- we have a professional project management / delivery office, and all of our engineers must take 5 project management (2-4 hour, in-house) classes, but other than that. PMP is not needed.
However, all of the others in the Project Delivery Office who are NOT engineers, but working at the same Project Manager (aka highly paid) roles, seem to have their PMP, and are excellent at their job and know how to use the tools better than the engineers (and they get paid better the better they do).
The students in my class, from non-engineering backgrounds, including hospitality, IT, event planning, construction, health care find the PMP immensely valued in their organizations and for their careers.