For most encounters in the open world that even makes sense. You don’t want enemies chasing players across half of the map. Especially if you can have enemies that are faster than the player. Fence them so that they will eventually give up if a player runs away. This also helps if a player doesn’t want to constantly combat and would have to constantly sneak through the map (or exclusively fast travel).

But two points to make this less cheeseable:

1. for bosses - make sure that there are spots that are relatively safe to e.g. craft ammunition, catch a breath, develop a plan, scan its weak spots,… but don’t make it 100% safe. The boss may be able to snipe you from some areas, so you might be moving around some rock to constantly to stay out of line of sight or such. Find an „excuse“ on how to make the whole map accessible to the attacks of the boss and (at least for real bosses) how to lock the player in. Make the auto save before the lock down, not after.

2. for other enemies: don’t fence them in a specific spot and create an invisible border. Better: define a point on the map as their home. They may chase the player, but randomly decide at which range X+-Y% from that point they rather return home. Also randomize the time it takes for them to loose interest in you after loosing LOS. That way it’s not an obvious invisible border you can abuse- more like a zone in which they will probably stop hunting you. Maybe even combine that with other data like- is the player generally sticking around and trying to kite the enemies to some location (and trying to cheese combat/an objective) or is the player just running straight away indicating they stumbled upon the enemy but have no interest in fighting.

In the end - a game is not realistic but a kind of simulation. Do what looks cool and feels right and is fun. Not what is realistic - if you were to sneak into a camp of the army, they probably won’t stop searching you after a few seconds when you slip around a corner after they saw you…