When you get your Professional Engineering license. You also get the PE stamp which allows you to approve public projects.
When you give your stamp of approval on a project then you're legally liable for it.
You can be sued for incompetence. Then, you have to go to court and defend yourself. Or, more commonly, your company will send a lawyer but you still may be called to testify.
List of Engineering Disciplines that can take the PE exam:
- Agricultural and Biological Engineering
- Architectural Engineering
- Chemical
- Civil
- Control Systems
- Electrical and Computer
- Environmental
- Fire Protection
- Industrial and Systems
- Mechanical
- Metallurgical and Materials
- Mining and Mineral Processing
- Naval Architecture and Marine
- Nuclear
- Petroleum
- Structural
It's a really hard task to compare engineering to plumbing.
I mean the board that licenses Civil Engineers, for example, should be very stringent. We don't live in buildings that aren't structurally sound or drive on half-assed bridges.
Professional Engineers hold themselves to an ethical standard that they're not even legally required to uphold, yet they still do because this organization keeps them in check.