I have not tested this, but if you want to save space, it may be an idea to rebuild packages....
Afaik the pre-compiled packages (except for what is in the FPC folder) come with debug info. That eats into space. If you do not intend to debug into the LCL, you can rebuild this.
In all folders, EXCEPT any folder inside the FPC folder, remove all *.ppu and *.o files
Make sure debug info settings are off for each individual package.
Make sure Tools > Config build IDE does not have any debug info (-gw -gs -g...) set
Next rebuild of your project will take a bit longer, as it recreates some of the deleted files.
There may be some files that are not recreated, if they are not needed by your project(s). So that would save space.
I guess (but really not tested) that the recreated files may be smaller.
Each time you install a package you rebuild the IDE, that leaves ppu for the IDE (and IDE only packages). So you need to clean out again.
It is full intend they are left behind.
It save cpu time for the next build. And with that it save energy and is better for the environment. (Well that depends how long you keep them till the next package install, and how big the impact on producing the extra storage is / assuming you can otherwise re-use the storage for other purposes....)
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No idea if or how much that will save...