Not all plumbing is the same. A residential plumbing service will handle different tasks and see different things than a commercial plumbing company. This video explains the difference between the two types of contractors.
Residential plumbing repair jobs put a contractor in multiple sites all across town. In fact, a residential plumber will likely go to new sites multiple times a day. They will see a lot of different issues, too.
The benefit to being a residential plumber that works on new homes being constructed is that there is no lack of new homes. They are always popping up and the contractor will be able to compete with other companies for a wide range of jobs.
Commercial jobs are much larger and the plumbers working on them will spend a lot more time on one site at a time. You have to have a strong eye for detail because there are so many moving parts. Each part of the project will be done in sections, and there will be a lot more people working everywhere on the site at one time.
Commercial service jobs will take you to a lot more sites because the work is not so involved, but you still may end up with larger projects. For more information, watch the video in the link above.