PlasticSCM Professional supports the concept of Access Control Lists (ACLs) for every single object defined in the system. This gives companies total freedom to choose any security policy, not being restricted by tool limitations.
If yours is an open environment, then probably security is not a big concern. When a development group becomes a team setting barriers with security is not a good idea. Still, there are always certain assets to protect, depending on the different people accessing your system.
There are also many projects in which having such an open set up is not a good idea: staff mobility, big amount of developers, junior staff, among others, require a more secured SCM deployment.
That's why in Plastic SCM Professional the security mechanism allows full customization. Everything is possible, from disabling security or giving default access, to fine grane tuning on a per-object basis.
For companies involved in quality validation processes like CMMi(*), it is often required to provide a given level of access control for project assets, which can be easily implemented with Plastic SCM.

Capability Maturity Model Integration (CMMI)® is a registered trademark of Carnegie Mellon University.