The InDesign pasteboard is the grey area surrounding your document pages. It's designed for temporary storage — elements you're considering but haven't placed yet, alternates you're keeping around in case the client changes their mind.
In practice, it becomes a graveyard.
What accumulates
Draft headlines from three versions ago. Image placeholders you tried and rejected. A colour swatch you tested on the pasteboard before applying it. An entire alternate layout you built in week two and abandoned in week four. A client's raw photo that got placed incorrectly and then moved to the pasteboard "just in case".
None of this is visible when you're working on a page. It sits just off-screen, invisible but present. Every object on the pasteboard adds to the document's file size. Links to pasteboard images stay live. Pasteboard text frames with missing fonts trigger font-missing warnings. Pasteboard objects with unresolvable links generate preflight errors.
When you hand off a file or archive it, the pasteboard comes with it. I've inherited documents where the pasteboard collection was larger than the placed content.
The manual approach
You can select pasteboard items manually. Press Escape to exit any text frame, draw a selection rectangle in the pasteboard area of a spread, and delete. Repeat for every spread in the document.
This works but it's tedious on long documents and easy to miss spreads. There is no built-in "select all pasteboard items" command.
The script approach
The InDesign scripting API exposes a parentPage property on every page item. If parentPage is null, the item lives on the pasteboard rather than on a page. Iterating through doc.pageItems and removing anything with a null parent is about five lines of code — and it runs in a second or two regardless of how cluttered the pasteboard is.
Nuke Pasteboard Clutter does exactly this. No dialog, no list of what it found — it removes everything off the pages and confirms when it's done. It's available free on the scripts page.
When to run it
Before archiving a file. Before handing off to a printer or client. When a file has grown inexplicably large. When you inherit a document with an unusual number of font-missing or link-missing warnings that don't correspond to anything visible on the pages.
Building the habit going forward
The pasteboard accumulates because moving something off-page feels safer than deleting it. Rarely is it. InDesign's history handles accidental deletions during an active session, and any file worth keeping should be versioned at the folder level anyway.
The mental model that helps: the pasteboard is temporary working memory, not a filing cabinet. Things go there while you're deciding. At the end of a working session, anything that didn't make it onto a page gets deleted, not stored.