I have been on the Michigan State Board of Professional Engineers since 1989, and I was chair for the 1995-96 year. I helped develop the new format of the Fundamentals of Engineering (FE) Examination which was administered for the first time in October 1996.
With regard to the advisability of obtaining licensure, it is true that many corporations do not expect their engineers to become licensed. However, with today's increased mobility of professionals, who may work for many different employers during their careers, the PE keeps more opportunities open, including private consulting. And, it is much easier to take the examinations as soon as one is eligible, upon graduation for the FE exam and after four years experience for the PE exam.
Another point in favor of licensure is its validation of the engineering credentials of the licensee. Unfortunately, many people hold "engineering" job titles who do not meet the educational or experience requirement to be a professional engineer. The PE license makes it clear that this person has an engineering degree and professional engineering experience.
In the past, mechanical and civil engineers had an advantage in taking the FE exam. The new format, however, allows for a choice among six exams. The morning section is the same for all candidates, covering the introductory topics found in most engineering programs. The afternoon exam is selected from among six disciplines - chemical, civil, electrical, industrial, mechanical, and general. This allows examinees to be tested over topics from their upper level undergraduate courses.
There are some states which do not license by discipline. In fact, the Board allows candidates to select any licensing exam regardless of their degree. However, all engineers are bound by ethical principles to practice only within their area of competence. Licensing by discipline would not change this situation. Even a licensed mechanical engineer might be capable of designing HVAC systems, but would not be competent to design automotive transmissions.
In conclusion, the licensing process exists primarily to protect the health and welfare of the public. It is incidentally also a means of recognizing the professional competence of engineers. I strongly encourage all engineering professionals to obtain the PE license.