Hi Robert,
No problem. Happy to help!
You can either have them hinged together, or you can also have it so one board sort of bolts on top of the other (usualy with assistance from removable end plates [a square of thin ply maybe] or other removable support). I suppose it depends on the size of the layout. Whilst hinging is possible, on a 6ft layout with 3ft boards it might get a little awkword.
It makes it easyer to transport (if you also have fold in legs fitted to the boards it literaly means you only have one thing to carry for the layout. Rather than making several trips with multiple boards and trestles) and does indeed protect the layout.
Aspects of Modeling - Baseboards for Model Railways. By Ian Morton talks quite a bit about portable baseboards, I'd recomend you get it. It helped me out loads.
Hope this helped and if you have any more questions don't hesitate to ask, I'm always happy to help!
Heinz