It’s a good time be a Star Trek fan. Strange New Worlds is great. So in case you want to play Modiphius’ Star Trek Adventures or some other Star Trek RPG, you might run into certain questions about space and navigation. Especially: Why do they have battles in open space? How can you blockade a Romulan fleet with a hand full of ships from reaching Klingon space? What even is the probability of meeting anyone?
Rest assured, Trek canon has an answer. Space isn’t empty. Of course there are visible phenomena like the Badlands, but in the TNG episode Force of Nature we learn that space is navigable only in a small corridor around the Hekaran homeworld. Data has a presentation and explains that ships cannot travel at warp outside the corridor.
The Hekaran corridor might be an extreme case, but we see that there is good space and bad space in terms of warp travel. So whenever they appear to be defending strategic points in space, they are actually defending some piece of good space.
This also makes navigation a much more complex task. You cannot just go in a straight line towards your target. You have to avoid bad space. And if you want to account for erratic travel times in the shows (even when they take the same way back and forth), just assume it’s not a binary distinction. There is space that is more or less amenable to warp traffic, maybe even in a way of going uphill and downhill.
It can also explain some other weird numbers like the Federation stretching over 8000 ly. The number is big. Like the milky way is 1000 ly thick. And also ly is a measure for length, not for area, or volume as we might expect to describe the size of a 3D political entity. So what Jean-Luc is referring to might be 8000 ly of warp highways the Federation controls.