Question

Or they (team members) need someone to keep pushing?

Edit:

1. The above line was supposed to be sarcastically funny. Sorry to throw you guys off.
2. I am talking more in the lines of distributing that work within the team, and not having one person assume and/or perform project management activities.

Answer 1

You may not need a project manager as an exclusive role (depending on the size of the project in question) but you do need someone to track activity and make sure everyone is reaching their objectives, and assign extra resources to bottlenecks. In a large project, this is a full time job, and you would need someone just for that. In smaller projects, one of the team members can do this in addition to their other contributions. Of course, the project manager is, in fact, a member of the team, but I assume by team members you refer to the computing group.