Why Is My File Size So Huge?
I have a 60+ page CS3 file that saves at around 450MB and growing. Doing a quick preflight check shows that there are no embedded images nor saved image previews. The linked photos themselves are high resolution, around 2-3MB a piece. If it's not saving any image data and merely linking 500 .jpg images, why would this file be so large?
Ironically, I know the answer to this one because of my long history with QuarkXPress, which also exhibits this curious phenomenon. There are a number of things that can make your InDesign files huge. The first thing to always try when trying to reduce file size is to choose File > Save As. That clears out any gunk that has accumulated while you've been working on the file.
However, in this case, the problem is, in fact, your images. These images were probably saved from a digital camera to disk, and then imported directly into InDesign. Unfortunately, many cameras save their files at 72 ppi (pixels per inch, sometimes called dpi). It may be a 17 MB, 3000 x 2000 digital capture, but if it's saved at 72 ppi, then it's about 41 by 27 inches large. So you import it into InDesign and scale it down to the proper size, which increases its effective resolution (watch the Info palette to see original vs. effective ppi).
Now here's the rub: When you import an image, InDesign saves a low-res "thumbnail" preview of it, right? That's what's stored in the InDesign file itself (so you can still see the image if the original on-disc image is missing). But when you import a 72 ppi image, InDesign saves the entire image as the preview! It essentially embeds the whole thing because it's trying to save a low res (72 ppi) version of your 72 ppi image.
The solution: Open your file in Photoshop, choose Image > Image Size, turn off the Resample Image checkbox (if you don't want the image data to change), then set the resolution to something reasonable (such as 225 or 250 ppi). Now save the file and reimport it into InDesign. InDesign places the image at the proper size, makes a much smaller proxy image, and the next time you do a Save As, your file size should drop considerably.
Sure, there are other reasons that InDesign files can get huge, but images are the main problem I've encountered.
(By the way, I discovered why InDesign files jumped in size between CS and CS2: Color management was turned on by default in CS2 and InDesign started embedding CMYK profiles in its files. A CMYK profile may be 1-2Mb in size, so the minimum InDesign file size--what you'd get if you just had an empty INDD file--suddenly got much bigger.)
By the way, Ben later replied:
A quick batch in Photoshop helped me to fix these up to about 180dpi at no larger than 8 inches in either horizontal or vertical. The file size wasn't decreasing until as you suggested doing a simple Save as. Sometimes it's the slightest things that can trip you up.