The first situation which he labels as 'Task Oriented Project Portfolio' deals with multiple projects that are very short in duration (a few hours of 1-2 days at most). The basic problem in this situation could be that there are a lot of these small projects and the PM has a full-time responsibilities on top of these projects.
The second situation is labeled 'Independent Project Portfolio' where there are a lot of similar type projects that are not related (no dependencies between the projects). The problem here is resource availability that is fixed but there ends the dependencies between the projects.
The third situation is called 'Interdependent Project Portfolio' where there are large projects with many small projects identified as tasks in the large projects. Here, the main problem is the different kinds of expertise that is demanded of the resources under the overall time constraints. An example of a move is utilized where it is a large project with many sub-projects that have time dependencies but are not related in content (computer setup, ordering utilities etc.).
Entrepreneurs in start up companies especially run into the first situation where there are so many of these small projects that the business owner is just plain overwhelmed. I have recently found myself in this situation and I was very thankful to read Dobson's book and apply the simple techniques and worksheets provided in the book.
Dobson briefly develops the circumstances surrounding each type of multiple project scenario and provides techniques and worksheets that a PM can use to manage in each situation. He also creates new definitions that apply in these individual scenarios.
This is not an in-depth treatment of the complexities involved in handling multiple projects. The book is only about 134 pages long. It is an expensive book but I would highly recommend any serious project manager to at least borrow the book from some PM library that you may have access to. Dobson also spends almost half the short book on explaining simple project management concepts like WBS, Gantt Charts, etc. that most project managers are already familiar with. Hence it makes for a very quick but valuable read. Don't miss out on these neat techniques. The ROI is very high.
Michael uses clear reasoning and definitions backed up by proven methods eg. PERT and CPM. He defines projects into portfolios and gives sound analysis for scoping and reasoning. The book distinguishes the juggling between Task-Orientated Project Portfolios, Independent Project Portfolios and Inter-Dependent Project Portfolios.
This book even covers the distinction between urgency and priority which is a issue for all Project Managers.
Excellent reading and comparatively light reading for a book rich in information.