Here's why I say that...
Nice, calm, frequent customer interaction breeds client trust. The loud demanding project manager can take a seat. Customers want to be courted. They want to at least feel like they are in control...even though they really want you to be controlling the project. I guarantee you that they really don't want some loudmouth jerk calling the shots and telling them what to do. And you don't even have to be a loud-mouth to turn them off...arrogance works well, too.
Project team members respond better to nice guy project manager. Our project team members like to be treated professionally. When you do so on a regular basis, they are very willing and pretty dedicated to give you their best. And during those emergency times when you might seem to be a little more demanding than usual, they are ok with that because they can discern that behavior from your regular management style and understand the situation for what it is...possibly dire. And they step up to the plate and do what is needed because they respect you rather than fear you or just be annoyed by you.
Senior management doesn't really like the squeaky wheel. You'd be surprised...your senior management may respond to that squeaky wheel, but they don't necessarily like to deal with them and only keep them around because they are good at what they are doing and the organization needs their skills. If that person begins missing obligations or upsets a project client, they are likely gone fast. They much prefer to work with the individuals who treat their peers and customers with respect and don't go around complaining and micro-managing all the time.
The easy to work with creative project manager can make connections in the organization. The nice guy project manager has an easier time making allies in the organization that help him get his job done and the keep the project on track. I've always been successful making good connections in accounting to get fast financial data on my projects while they are in progress...thus helping me to do accurate and timely financial analysis of all of my projects' budget health status' every week. No pulling of teeth to get up to date time charging information and get any necessary corrections made quickly so I can get the right data out to my stakeholders. It has also helped me numerous times get the right person hired through human resources contacts when I'm hiring directly or get the right person on my project team when I'm working with the organization's resource gatekeeper for project assignments.
People do stuff for the nice guy creative project manager. One final general thought...people are more open to just doing helpful things for you. Managing a project is demanding. Often times we have to boss people around and demand information, extra work, decisions, help, etc. from those working around us and with us. When that demanding behavior is an exception and not the norm, those individuals around us realize that it is a real need for the good of the project and not just us demanding something because that's how we are. And, likewise, they are more willing and ready to help us on a moment's notice. Don't purposefully take advantage of it, but it truly works when you need it.
Summary / call for input
Here's my motto – treat those working with you and for you as you want to be treated and life will be easier. Jobs will be easier. And you'll get more work done and more cooperation doing it. I'm sure most of you are already practicing this...but if you aren't, then try it and watch things change for the better around you and on your projects.
How about our readers? Where do you think the nice guy project manager fits into the world of project management? Does he get things done and get ahead? What's the climate in your organization?