Standing/sitting practices of an instructor
Does it effect teaching success in any way?

Effective teaching engages with students.  If there are many students, you cannot engage with all of them effectively from one place.  For example, I walk to the part of the room where students are not paying attention; then they start paying attention.  I do not recommend either standing still or sitting still; sitting in a moving wheelchair would work fine, though.  That's not quite what you asked for, but it works.

Is this rule implemented in the institutes of many countries?

I've never heard of it.  I think this rule would be illegal in countries that protect workers with disabilities.