Basics and limitations of multi-tile terrain in 2018.3?

Could someone explain to be the basics of using a multi-tile terrain in the new 2018.3 terrain system?

I'm working on an RTSish game and would very much like to benefit from having a bigger map, divided into sections, but am I correct in thinking this won't work, because:

1) if I move the camera away from one of the tiles, it's gonna stop being rendered but also the units will start falling through it's floor, and navmesh will stop working for that tile? Is that the case or am I talking silly?

I could find tutorials about using the system, but nothing about it's actual ground-rules.