ditzyboy,I assume you are talking about a well known LCC in OZ.In that case I agree with you that it is faster especially if you have families and people with special requirements boarded first.
The only problem is that it also caused some vocal arguments and was quite funny to watch at times but then I wasn't crew so didn't have to deal with it.It never ceased to amaze me how infantile people can be and the pushing and shoving was a sight to be seen.It was supposed to save the airline money but it must have caused problems because they changed to allocated seating.
The funny thing was that the first on board thought they were being smart and usually grabbed the first seats they could see and that left the overwing exit seats with more legroom free for those of us who knew about them.
Pity they went to an allocated system.