The first obvious difference is at the team member level. They will not only have two "bosses", but they will need to start reporting in project management concepts:
- how long will it take for a specific activity to be completed (estimation)
- what progress has been made on the current activities and when they will finish (time to completion)
- if there is a deviation from the estimation, what actions can be pursued to correct it (financial management)
- what risks and problems are foreseen at the technical level (risk and problem assessment)
- what scope deviations are foreseen at their own level (scope management)
- what technical arguments can be given to persuade the client to chose a certain solution or to understand scope deviation (client management).
Staff in companies that are young from the project management perspective try to resist providing all these information to the Project Manager. They see it as overhead talk. They believe good Project Managers should be able to know all this and do their own stuff without impeding other's work. But what good Project Managers should do is to try to train their team members and make them understand what is required from them in order for the project to work well. The reality is that Project Management does not work if only the Project Manager practices Project Management.
The second obvious difference is at the managerial and support level. For the Project Manager, everyone is a resource in their project, and as her ultimate goal is to make the project successful, she sees Management, Accounting, Sales, Purchasing, Logistics as entities that should cooperate for her project's success. Unfortunately, Management, Accounting, Sales, Purchasing and Logistics don't see themselves in the same way. They often have different agendas that no doubt are important, without realizing that failing to cooperate with the Project Manager results in blocking the project and wasting the work of the PM or an entire team, the fury of the client and delays in obtaining the revenue used to pay their own salary in the first place. This is why Project Management is a practice that is to be internalized by the entire organization, no matter the role in the company.
In some of my recent work, I have put a lot of emphasis on developing a Project Management book aimed at managers and executives and I plan to actually transform it in a course. You can find extracts from the book by searching for the tag "Project Management - a managerial approach". The concept of Project Management with a managerial approach is the same as with any discipline taught in MBA (e.g. Macroeconomics with a managerial approach, Accounting with a managerial approach): a discipline with a management perspective that is as technical as needed for a manager to be able to manage specialists and make the most benefits of it. I plan to continue with some articles on Project Management aimed at Accounting, Sales, Purchasing and Logistics.