@VisitorsFromDreams
It depends on how you implement it. It depends on what you use as the triggers for it. A Quest to "clear out a cave" would make the cave appear, but it would be on a return trip through the area. It wouldn't happen after you just left the area. You would leave the area, do some more main storyline, maybe move to the next area... then there's a Quest that says there's a cave that needs clearing and where to find it. So, you come back, you find out that there's a new cave. Maybe there's some lore associated with why it's just now showing up.
It depends on how you handle things. How much time the player
perceives has passed between events.
It absolutely does not work in the same instances that the "Roadblocks" normally work. As in, you pass by the road block, do the minor quest thing they want you to do, then come back and it's suddenly open. It wouldn't work in such an instance as it's literally doing the same thing as just having the immersion breaking road block to begin with. However, if you never realized there was a path there, you did some more Questing, a few main story things, and came back into the area... and someone tells you there's a path? It works. Especially if given a modicum of explanation for where the new path comes from.
One of my games uses a different method for it and simply has the world map as "abstracted". You go on a Quest, it tells you the "area", you select it, and sometimes you get a menu of locations to visit from that area. Likewise, it's also abstracted in that sometimes years have passed from the time you first visited a location and you've come back to it (it's a game that takes place in about a 30 year span or so, with the player engaging in large chunks of that time).
I simply prefer the "immersion" to the absolutely silly, "Yeah, it's blocked off until you hit the Main Story trigger to unlock it for you". It feels arbitrary and unnecessary. It feels artificial in a way that you're trying to keep me from breaking your game because you didn't have the foresight to predict a player could break it if you didn't include the roadblock.
Some of the most interesting things I've seen games do is let me go where I want... and then respond when I've "done things out of order". Like, for example, the Deus Ex games. Games that acknowledge you did things "out of order" and you're rewarded for pushing through a challenge despite obviously not being up to doing it.
I simply prefer games that don't obviously road block me, and let me go anywhere I can see. Games that don't tease my sense of exploration. I really hate that, "sigh, I guess I have to come back here later... there's no reason to explore anything right now, since I'll be coming back in like an hour anyway" idiocy of map design. It's something even Pokémon has engaged in with the last 6 games or so. It discourages any exploration by telling you that you'll be back later anyway, so explore later, once the entire path has opened up for you.
It's just not fun.
The only exception to this that I enjoy is a "Metroidvania", but it has to be designed well. That is to say, almost every "roadblock" in the game isn't a main path. It leads to some sort of minor upgrade that you can choose to ignore or choose to pickup later. Each "roadblock" is simply unimportant and is just a means to tell you, "Hey, come back later when you've got X Power". Likewise, these locations offer a small challenge in some way. I like those sorts of Road Blocks. They reward me for remembering the locations exist, reward me by challenging my skill when I find them, and give me a minor inconsequential reward that I can skip if I really don't care.