On software projects, people with specialized skills work. Some people have experience in gathering software requirements and creating software requirement specifications. So they work in software requirement engineering parts of the software project. Some other people have experience in creating software designs like object diagrams, statechart diagrams etc. So they work with tasks associated with software designs. Similarly people with skills and experience in other tasks related to developing software products work in their respective domains on software projects.
All of these activities of software requirement engineering, software design, software construction, software testing, software release, software project management etc. come under software engineering. Students who learn software engineering, learn about all these disciplines which are part of software engineering. But what about software professionals? If they have to learn all of software engineering and its constituent parts?
Generally a software professional acquires skills and experience in any one discipline of software engineering and gets a job. The software professional keeps working on the same discipline for his/her entire career. But not all software professionals keep working in the same discipline during their entire career. Many software professionals move from one discipline to another at some time in their career. Many more software professionals acquire expertise in more than one discipline.
One other consideration to understand other disciplines of software engineering is that it helps in understanding your own tasks. If a software requirement engineer understands how software designs are built then he/she will be able to create better software requirement specifications. It is because, a software design requires good software requirement specifications. Likewise software construction requires good software designs. Understanding other disciplines of software engineering definitely helps project team members to do their own jobs better.