Nej, you're not alone on that boat.
Main reason why I dont really join any groups all that much is because I dont see how I can balance out my time for the group...OR I just haven't found one that interested me.
When it comes joining the site / downloading the map, I'm guessing it's to keep order and so that way it's more organized to them and will avoid having to repeat themselves, everyone will be accounted for, yada yada.
But hey, everyone is different so what might work for some, might not work for others.
Interesting topic though c;
I honestly don't mind if groups have their own sites/maps and whatnot. I am with a lot of other people here though when I say I have to kinda watch the group and see what they are all about before I consider joining them.