As a modeller, you sometimes need to consider different ideas to the one you had originally chosen, especially when modelling areas within the layout.
I'm currently working on a small station yard for Elkin Station, this then leads in to the copse area by the tunnel. I had originally wanted to place an old vehicle wreck within the bushes at the back end of the yard, however room was not adequate enough and I had to change my idea a little.
I still kept the general idea of the yard, but adapted my idea around the space, my wrecked vehicle will go somewhere else now.
Another aspect in flexibility is to see how different ideas and models might work when presented. I had originally decided not to have houses on the layout, this has now changed and some houses are now included replacing the original idea.