I recommend reading the guide linked in above post, but the shortest way to explain difference:
RegularWorks like you expect a gate would work -if it is closed, you can not go through it. When it is open, you can, and there are no string attached other than somebody closing the gate and trapping you inside.
VisitorThe one with not so intuitive but necessary rules attached to it.
- Even if it is open, you can not pass through if you have an active combat relation. (You need to drop combat entirely, just toggling peace/yield is not sufficient.)
- If you do pass through and the gate is covered by claim(s) you will gain Visitor status to said claim(s) until you leave the claim(s) entirely. (You need to walk to an unclaimed area to drop Visitor status. This leads to potential security hole in a village, a literal "hole" of unclaimed land in the middle of village where you can drop Visitor.)
Clarification: gate does differentiate you going in/out in any way; going too close to gate's hitbox from either direction will simply apply the Visitor status.
Why do we have this complicated mess?
It used to be simple system, only regular gates except you gain Visitor as you do now from V-gates. Unfortunately it led to this:
[I don't have easy access to the image, but imagine a 10x10 palisade box made entirely of sideways gates (possible by excessively building and bashing corner posts.)]
Oh, someone lays a siege on you? It would be shame if they could build a safepali where to run if they need to flee, and if you come inside you can be instantly KO'd with "Evict" (at least I think they only later added a countdown timer to Eviction.)