So why would someone want to become a Mechanical Professional Engineer? Well, there are a variety of reasons.
First, by becoming a Professional Engineer, you are stating that you possess knowledge and an experience level necessary to effectively practice engineering. This gives prospective clients and employers a "quick reference" to the level of your competency. It will help you stand out from the sea of applicants when interviewing for a job. An employer will be able to quickly recognize that you are skilled in the art of engineering. In an economy which is rapidly growing more competitive, the ability to make yourself stand out and be unique is very valuable.
Another reason is that you will get paid more! By adding this extra qualification to your resume you are instantly more valuable to employers. Once I passed the PE I received an instant 15% raise and pay grade bump at my employer.
Yet another reason is that you will have the ability to start your own engineering design or consulting firm. A PE license is a requirement to start any type of engineering firm. You will be breaking the law if you start a firm without one.
One perk you could take advantage of only by being a PE is that you could be asked to act as an expert witness in a courtroom trial. Professional engineers are recognized in the law community as people possessing a higher degree of knowledge over a typical engineer and could be asked to lend their engineering opinion on a case. This opens up another income avenue for Professional Engineers since they are paid for any time they spend being expert witnesses. If you ever decide to testify on a case, your skills and PE registration could play a deciding role in the courtroom.
At your present job you will have more respect from fellow engineers. People at your job will recognize the significance of your registration and value your input on engineering matters.
If you want to move up the corporate ladder (and who doesn't), your potential for career advancement is far greater when you are a PE. Most management positions in engineering require the person to have a PE.
In addition to furthering your career in the business world, obtaining your PE will allow you the opportunity for teaching in the future. Many universities require a PE license to teach.
So there you go! I hoped I've sufficiently persuaded you that obtaining your PE will help your long term career and earning potential. It is something which you will not regret earning!