The importance of a large grid depends on the context and setting of the game. Ironically, the larger the scope, the less likely one needs a large grid.
For your average WoD game, I can understand why people want a GRID. Walking around the streets is a somewhat important element to the game that is often forgotten.
For a game like, oh, Mass Effect, you'd probably want modular places. On the Citadel, large areas like "the Zakera Ward" need no Grid; it's probably enough to attach rooms to that one room, and allow people to "Rapid Transit" between areas.
For a game like, oh, Dragon Age, you'd probably want to do the same thing as Mass Effect, but you could also add rooms to represent other "zones" in a region, wherein there may be pitched battles.
And then, if you have a space ship, you'd probably split the rooms into general floors/wings, with rooms sprouting off of them. Space stations, the same.
The game designers have to consider where they want the RPing to occur. If you want a lot of backdoor, small-scene, schemes, like in a Lords-and-Ladies game, having a detailed, large Grid would be helpful. If you expect there to be a lot of pew-pew-pew, with less importance on social scheming, then having rooms representing areas of larger scale is probably best. Take into consideration setting, and you should have an idea of how to lay out the Grid.
Note, though: being too abstract often leads to confusion, as occurred on Victoria Reverie.