From the old forum, someone asked about the java.util.Map<java.lang.String,java.lang.String> renderingParameters parameter in ComponentPresentationAssembler's getContent().
Nuno Linhares suggested this might be optionally used by XSLT Component Templates (CT). CTs set to XML Document can store run-time XSLT which might use parameters like Publication ID and others.*
I'll add that this needs to be via ComponentPresentationAssembler rather than ComponentPresentationFactory. These XSLT CTs are distinct from modular templates using the XSLT Mediator (see the docs). John Winter also asks about the XML Document setting and extra tab in this question.
In practice I haven't seen this parameter used (especially if Nuno said he wasn't sure). Though something like it could make a nice "enchancement request" for the Razor Mediator.
