Also, there's no reason why your sandbox campaign can not also be a "points-of-light" campaign.
When you play online games such as Bardur's Gate, and you have to get from one "area" to the next, does it matter how far A to B is? To me, all that matter is that you got there unhindered (or not) and you're off on your next adventure.
I use "points of light" in a different manner. To me, it means little islands of relative civilization and safety amidst the unknowns and danger of wilderness. This is pretty much the default setup of the "wilderness" in the original D&D books.
For example, a typical domain might include a lord's castle and a handful of attendant villages, with the influence of the castles stretching in a twenty 20-30 mile radius. (The villages would be within that radius.) Traveling within that radius is relatively safe.
There might be a handful of other such "points of light" on the map. However, the wilderness area between them is just as important as the points of light, themselves. In fact, without the "darkness" of the wilderness, their significance as "points of light" is completely lost. It absolutely *does* matter how far it is from point of light A to point of light B. And getting there can be an adventure, in itself.
The thing about a sandbox game is that the setting isn't just a backdrop for your adventures. Instead, the setting is an integral part of the game (in a "gamist" way, not in a story setting way). In a real sense, you "play" the setting. With that kind of approach, glossing over things like distance, travel, time and resource management isn't desirable.
This kind of approach is especially satisfying when incorporating the traditional "end game" that takes place around name level in the TSR editions. Setting up a stronghold isn't just a cherry on the top of your character's story, but a gamist accomplishment, in and of itself. In fact, you might even say it's a way to "win" (not exclusive other ways to enjoy the game or succeed at it, of course). When the game setting has real context and meaning in game terms (time, distance, population/military/income resources, etc), the "end game" of setting up a stronghold and becoming a lord among men becomes a satisfying game accomplishment. (Also, while the "end game" only fully develops when the PCs have become more powerful, it can start at the very beginning.)