You can basically have different permissions or operational behavior configured for iterations like you can do this in team area hierarchies. E.g. you can prevent roles from delivering code in an iteration (or the last days of an iteration, if you add subiterations that don't have a release planned) while other roles can.

See: Process permissions lookup in Rational Team Concert 2.0 and Process behavior lookup in Rational Team Concert 2.0 for how that works.