When a lot of us do the Main Scenario Roulette, most prefer to run through it and get it over with (as it is a tedious one to do after all). Occasionally there will be first timers, and although its no different to it happening in any other duty, the main scenario ones are quite cut-scene heavy but do actually relate to the story.

I think its alright to go ahead if anyone else in the team can at least update the newbie on where to go, or what do do/switch to press etc, it's easy to get lost in either of the scenarios. But there are many occasions when that doesn't happen, i.e. a tank might suddenly become a dictator pulling everything ahead as they go and shooting down anyone that questions it. Many times I have heard "we only need 3 people to run this", or "x person wasn't needed anyway" etc. You'd think with such salty attitudes you encounter in there sometimes that you were doing Extreme or Savage content!