When you move a machine from one project to another, the machine is not automatically rebuilt. It still runs the same profile and all the same software it was running in the original project.
There can be reasons for wanting to move a machine between projects without rebuilding it. For example, due to a reorganization, the same users and hosts may be providing the same service, but under a different department or project.
If the old project was running processes on the machine that you do not want, you will have to stop them manually.
Once the machine has changed projects, after a few minutes, the authentication will have changed so that users from the old project can no longer log in and users from the new project can now log in.
Existing user login sessions, however, are not terminated. Those users will not have root (UNIX) or Administrator (Windows) access any more.
The localadm group is used to maintain a list of users on the system who are local administrators. This group is not emptied when a machine moves projects. It could contain users which you do not want as administrators on the host in the new project.