When placing a really large dimensioned InDesign document into a smaller document the performance of that smaller document is crippled to the point where it becomes unusable, especially when there are many placed InDesign documents.

To test:
Create 4 different InDesign documents that are 3600 x 2580mm in size.
Create an A4 booklet with 4 pages.
Place a different one of the larger InDesign documents on each page of the A4 booklet.
Try and navigate from the first page to the last page of the A4 document.