If your project scope increases, you might need more time or resources (cost) to complete the additional work. When project scope increases after the project has started, it’s called scope creep. Changing project scope midway through a project is not necessarily a bad thing; for example, the environment in which your project deliverable will operate may have changed or become clearer since beginning the project. Changing project scope is a bad thing only if the project manager doesn’t recognize and plan for the new requirements — that is, when other constraints (cost, time) are not correspondingly examined and, if necessary, adjusted.
Time, cost, and scope are the three essential elements of any project. To succeed as a project manager, you should know quite a bit about how all three of these constraints apply to your projects.
Here is our final word about the project triangle model. Like all simple models of complex subjects, this model is a useful learning tool but not always a reflection of the real world. If real projects always performed as the project triangle suggests they should, you might see projects delivered late but at planned cost or with expected scope. Or, projects might be completed on time and with expected scope but at higher cost. In other words, you’d expect to see at least one element of the project triangle come in as planned. But the sad truth is that many projects, even with rigorous project management oversight, are delivered late, over budget, and with far less than expected scope of functionality. You’ve probably participated in a few such projects yourself. As you well know, project management is just plain difficult. Success in project management requires a rare mix of skills and knowledge about schedule practices and tools, as well as skill in the domain or industry in which a project is executed.