It makes you learn the geography of those places and how to better navigate through it, and as soon as you know lots of different routes, roads and interesting places in an area, it shifts the focus of the missions to the next area/city, which is almost always vastly different than the area you were focused before. I remember the first time you leave Los Santos and is thrown in the middle of Whetstone is when it hits you that the game is much bigger than you have seen up until that point, especially because of the way the game keeps its missions focused on certain cities/areas of the map at each point in the game's progression. The game never felt like it was this small. I remembered how shocked I was the first time I saw this post here on Reddit showing this image of the San Andreas map without fog or render distance.