The expensive part of a small craft project is sometimes the decision made too early: cutting a patterned sheet before checking its position, or gluing a decoration where the lid needs to close. A paper mock-up lets you make those mistakes cheaply.
Copy the footprint, not every detail
Suppose you are decorating a wooden storage box with three leaf shapes. Trace the lid, mark the hinge and front edge, then cut rough leaves from scrap paper at the intended size. There is no need to reproduce their colour or texture yet. You are testing the space they occupy.
Move the shapes around without adhesive. Try a centred arrangement, an off-centre cluster and a version with fewer pieces. Photograph each from the same angle. Looking at the options together is easier than remembering what you liked five arrangements ago.
Check the object while it is being used
Open and close the lid. Check the handle, latch and edges where hands will grip it. If decorations will stand proud of the surface, add temporary folded-paper blocks to suggest their height. A flat sketch can miss the place where a raised ornament catches the lid or your fingers.
Then place the mock-up where the finished object will live. A busy pattern that looks lively on the worktable may become difficult to read on an already crowded shelf. Leave some undecorated space deliberately; it gives the chosen detail room to be noticed.
Once the arrangement works, number the paper pieces on the back and note their orientation. Keep that plan beside the project while cutting the real material. Before attaching anything permanently, test the adhesive on a spare sample and follow its instructions for the particular surfaces.
The mock-up has done its job when it resolves a decision. It need not become a beautiful miniature project of its own.