Unfortunately this is a long standing issue (or bug) with the Stacks plugin and not something that we can fix in RapidWeaver Classic (I wish we could), but it’s up to YourHead to get a fix in for this one.
Okay, but why is Stacks making my files bloated?
Stacks is pulling in images from other open projects, partials, and externals and placing them into the project you’re working on. When you save the project you also save a bunch of those images into your project 
. Why it insists on doing this we’re not entirely sure.
To find out how much space is being taken up with this Stacks bug you can do the following on your project:
- Right-click “Show Package Contents” on the project file in the Finder
- Navigate to SharedPluginData > YHStacksPlugin
- You can Get Info on the YHStacksPlugin folder to see how much space this folder of random images is taking up
Here’s a video showing how to locate the folder - along with a glimpse at some of the crazy non-related junk images Stacks has saved into the project file 
In this project file those random images are taking up over 100MB, and the Stacks Contents.plist text file alone was 45MB. Seemingly none of the images are used in the actual project.
How can I reduce the bloat?
There’s no easy way to do this without possibly corrupting your project, and as it’s a Stacks issue we can’t really advise on removing those images as it could corrupt your file. To get this resolved we’d recommend emailing support@yourhead.com for guidance on how to do this!
It’s really frustrating that this is still going on after all these years as it affects every single RapidWeaver user that has the Stacks plugin installed.
We’re sorry we don’t have better news, but hopefully this explains a bit more about why it’s happening, and why it’s out of our control and not something we can fix 
Fingers crossed YourHead eventually get this bug resolved 