installing Durock prior to tile on walls?

Durock 3x5 feet on 5 foot side there is a thin edge. Do these edges mate up when installed? Can the pieces that have these edges removed be used or can they be modified, if so how. If not are they useable at all or?
Ernie

Mate em with a small gap, tape and thinset them even with the rest of the wall as you set the tile.