Like the Tiger's Mouth, the concepts of 'slow' and 'fast' are taken from the game of Go. Slow connections are stronger, whereas fast connections are more efficient.
If a string of drop uplinks are placed in a line, they form a strong, defensible wall. While I'm sticking to drop uplinks for simplicity, the wall could also include nanohives, installations and vehicles.
The more widely spaced these war assets are, the more territory they can claim. But the easier it is for the enemy to push through the line. These are fast connections.
The closer together the drop uplinks are, the more difficult it is for the enemy to break through. But the assets are being used less efficiently. These are slow connections.
There is no optimum spacing of drop uplinks - it depends what you are trying to achieve. Imagine that each drop uplink radiates an area of defensive influence. The further from the uplink, the weaker the influence. Slow connections provide each other with stronger mutual defense. Faster connections spread influence over a much larger area.
Very fast connections leave open the possibility for invasion. That is, there is enough room for the enemy to start putting their own drop uplinks in the gaps in your line. Invading is a large topic, so I'll leave that for future posts.
When you play Go, it is rare for an orbital bombardment to land on the board (although the Nuclear Tesuji is similar). But in Dust we must account for this. If drop uplinks are placed very closely together, they can be wiped out with a single precision strike. If you are using slow connections, it might make sense to spread them out a bit if you think an orbital is on its way.