And yet another save space thing is to clear the checkbox for "Store Drawing in the Project File" in the Drawing settings for each placed drawing (and the Tool itself for subsequent drawings). See attached.
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB One of the forum moderators
This sounds more like a question about the 3D model complexity than the base file size. The two are only very slightly related. You can have a tiny file that generates a huge model, and a small simple model with lots of detailed drawings can result in a large file.
If the model is too complex for the computer to manage whole you can use the marquee to reduce the extents of the model and layers to reduce how much of it is modeled. You can also reduce complexity by simplifying complex items like trees and such.
"I find that layouts can make the file very heavy."
Are you sure it's the layouts, not excess images/pdf's placed on them?
Anyway that's the way it seems here.
lec