Twilight checkin is basically just checking in your hold baggage the night before your flight and getting your boarding card etc.
Everyone in your party needs to be present with all your bags, including hand luggage!
Ideal if you live close to Gatwick or are staying in a local hotel overnight. You then can have a lie in and a nice breakfast the morning of your flight
The Virgin welcome meeting is a waste of time. It gives the Virgin reps. a captive audience to sell their excursions to
You will gain more information and tips from these boards than you will ever get from the Virgin meetings