Why we build card models before we draw details

At the end of concept design every client gets a card model of their project at 1:100 (sample).
Models show what plans cannot: how high a ridge feels from the garden, where the low winter sun reaches, what the neighbours will see. Clients pick them up, turn them round and ask better questions.
Changes at this stage cost an afternoon with a scalpel. The same change on site costs weeks.