Using this method only parts of the game world are preset like towns and major roads, zones between them however can be randomly generated.
A forest for example, the edge of the forest running along the preset main road is set already and doesn't change, however a few cells into the forest the terrain is randomly generated.
Within those randomly generated zones there can also be set zones like a old ruin for example.
The game could even create paths automatically by connecting point A and point B and then just create a road between them, if it meets a big obstacle it placed in the way (like a large boulder) it curves the road to go around it.
That way you could focus creative energy on detailing out a relatively small area and leave the "wild" zones open to be randomly generated from set seeds.
Also note I don't mean "it gets randomly generated every time you walk through it" but more it gets generated as you start up the game, it could save that as a BSA file you can simply use later on again to load your game from if you liked the area it generated. Or let the game calculate a new layout in which it could even be possible that some locations have changed position.