Thanks michael once again for your in depth reply. On your last post I would say there are three fragments. Perhaps rather than just having two sides as it were moi could temporarily auto group objects that have been split or partially split by the cutting object so here there would be three groups availiable for selection rather than a series of individual lines. This could be purely as an additional option on top of the current work flow. I remember working on a dummy test file and being frustrated by having to manually select the trimmed lines/objects - probably some sort of standing seam roof. Im often in two minds whether to use trim or bool in some situations as they often have the same outcome - which is no bad thing I guess.

Cheers