Risk assessment
Many issues can occur before, during and after the completion of a project that can affect the client's perception of its success. Knowing the risks that lie within a project allows you to take measures to prevent them from becoming an issue, or at least contain them from becoming more serious than they need to be.
Project nature
Not all projects are equal, and this is certainly the case when it comes to software projects. If you are creating an entertainment app such as a smartphone game, making the app enjoyable to use will be a top priority, whereas creating an air traffic control software will not have any emphasis on enjoyability and will instead focus more on issues such as reliability, scalability and fallback safety features for scenarios where system components fail. These examples show how diversified software projects can be, and hence how their relevant risks should dictate the style of project management.
Team politics
Most projects where there is more than one person...