[color=dodgerblue]If I may chime in.

Whenever I think of Sandbox Roleplays, I think of The Elder Scroll video games or Game of Thrones. Both have a large, fantasy setting that allows for multiple groups of characters to have their own story arcs at the same time without conflict. There is minimal amounts at best. Or at least that's what I'm led to believe. 

As for the attraction, I believe it's only for people who don't want the limited crawlspace of a set plot. I, myself, am part of that group of people who, while can go for a set plot game, also like that feeling of creative freedom that sandbox games allow. You can do your own thing and don't have to worry about anyone turning it down or say "oh, instead of that, let's do this." 

Of course, there are instances that this can totally backfire on someone. Case and point: what[@Nilesapa] said about too much world-building and how it could be a terrible illness for us creative folk. 

This is why I believe at least a minimal plot should be enforced. If not an organization, then maybe some monster or impending doom within the rp's universe coming. No one would know what it looks like or when it will come, but they still will have to face it at the end of the day. For example, in a DC sandbox game, something like Vandal Savage joining up with some all-powerful being or whatever you have it. Just something that every character, no matter where within the set universe or planet, at least senses is coming in the near or distant future and all must band together to fight the great evil.[/color]