A renderer is a program that turns websites into screenshots for the displayers to show. Dashman is composed of various different components:
You don't need a lot of renderers on your set up as they can server a lot of displayers. You can have one or many to for balancing the load and reliability purposes. The renders are the ones that have the cookies so they can access your website. Whoever has access to those computers will essentially have access to the websites you add to Dashman. Renderers should be secure by being locked with password, in a datacenter, etc.