You can apply one trap preset to one sheet of output, such as one page. Normally this is not a concern. However, if you print multiple documents in a book, and each document or page has a different trap preset, InDesign can resolve some trap preset conflicts by synchronizing presets among documents:

• If documents in a book use different trap presets with the same name, InDesign assigns the trap preset used in the master document, provided you’ve selected the Trap Preset option in the Synchronize Options dialog box.

• The synchronizing feature makes all the master document’s presets available to the other documents in the book, but does not assign them; you have to assign trap presets in each document, or use the [Default] trap preset. The presets appear in the Trap Preset menu of the document’s Assign Trap Presets dialog box.