No. In fact the opposite is true. The less bitmap images (jpegs) you have the better. Vector artwork (assuming your ai files are vector) are very small in filesize and will look pin sharp in any PDF as they do not need compressed.
Use PDF optimizer in Acrobat Professional. You can slim down your files alot there, and often find alot of waste with no sacrifice to image quality.
Hello Rik and Mike:
Really, Rik? I always thought vectors were large sized. Not sure where I got that from. So when vectors are placed into InDesign, they are small to begin with?
Mike, I did use Optimizer in Acrobat but I am not sure which settings are the best (for smaller pdf's) to use for vectors and jpegs other than setting both grayscale and color to 72dpi and quality "low" and I have every box checked in "discard objects" and "clean up" too.
I was able to get it down to 4 mbs (i'd like 3mb) with both Optimizer and Save as > Reduced file size in Acrobat. I was just asking about vectors because I wanted to see if there was something I could do about them to further reduce my pdf file size.
Most individual vectors are small, but size varies with complexity. Running the optimizer may not help by itself as vectors don't get compressed, but if there is transparency I believe you can create a custom flattener that will rasterize the vectors as well, and that may or may not yield a smaller file size.
Like Peter says, it depends on the file, but to give you an example, I used to develop a 170 page catalogue full of vector drawings. The logo for the company was in a jpeg and I could never get the file below 10mb - even with the logo looking awful. I changed it one day to a vector logo and the filesize is now 3mb and everything is clear. Doesn't work for every situation but I would always include vector instead of bitmap where possible.