Optically you can see from a region to the next one - the sim border is invisible. Physically though the next region does not exist until you travel over the border between the recent region and the next one.

Let's suppose you are traveling by boat. If you hit a pier in a region, your boat is bounced back. But if you hit a pier located on the next region reaching until the region's edge, your boat first travels over the sim border and suddenly gets caught in the pier bouncing like crazy.

Suggestion: the physics engine of each region should also load (render?) the physical shapes of the neighbor regions borders, which are pointed to the region, so a vehicle is bounced back and does not enter the next region where it is blocked by some object.

Advantage: physical experience would be far more natural, collisions on sim borders would not be special.

Since it is very common to build right until the sim borders, this is issue not a trifle at all imo.

Vessels that have a damage system responsive to collisions (to make sailing more challenging) use to sink immediately when hitting these sim edge builds (since being caught on an object causes plenty of collisions in a very short time), while they would only take some damage while hitting the same build from the other side.

This particularly is annoying, if there is a very tiny or even invisible object on the sim border, so you have no chance to recognize it before your ship suddenly sinks for no obvious reason.