I got to reading this artical at geyhawkgrognard as I've been planing games and doing my research and hobby'ing away I'm firmed up my stance on Sandbox vs Storyline and really I think they are really arbitrary distinctions. More a continuum.
Ultimately what is the point of filling a sandbox with story lines that many or may not get investigated. While this style of development give long term playability and is good for a computer game I'm not so sure its necesary or even a good idea for an rpg.
As I get older (just celebrated 41) I'm finding its much harder to get people to the game table on a regular basis so filling a sandbox full to the brim with "stuff"tm is just unnecessary particularly as time is at a premium.
So I'm starting to think the best approach is really broad strokes. Also I find players want to turn up, have their players meet in the tavern and the dark robbed figure says "venture forth for $$" and off they go. I'm oversimplifying but essentially the players I play with want to be up and gaming post haste. Honestly background - other then what is communicated in game - is often wasted on them.
So I'm leaning towards just-in-time campaign design. However I already know I actually like spending some of my time world building. Therefore I'll build the world but its going to be in relatively broad strokes only dipping down into the detail as I'm inspired to do so.
This serves the purpose of putting "story hooks" into the setting and they can be flesh out on the fly or by me during world building.
On the fly is good I think, mostly because emergent properties of play is a reality for the Players in a game so playing with in this framework is good cricket on my behalf.
Anyway there will be a "story" and the sandpit will also be there and if the players want to go off and do something other then the "scripted" adventure then I'll go with that too. The question is really "how" to do that.
As and addendum to the above;
It occurred to me these approaches are related to top-down and bottom-up approaches to information management. Therefore if storyline development is the equivalent of top down information management then the sandbox approach is bottom-up and a synthesis style approach. This is interesting as these therefore by extension would inherit the pros and cons of each approach.