I'm having a problem that by appending collections from scene to scene (or shot to shot) the blend files are inflating in size (well over 1GB already), although they contain more or less the same content. I found a ton of objects, images and materials in the blend file (Outliner>Blender File) which are not visible in the view layer nor viewport but only in the Blender file, and are often duplicates or materials and images from deleted objects or hierarchies. Purging does not get rid of them, and they are simply too many to figure out manually which ones are needed an what is garbage data. There is only 1 scene and 1 view layer in the blend file.
Finally I found a way do deal with this issue: Atomic Data Manager add-on for Blender by remington creative (free add-on):
It seems that I am not the only one who noticed that something is fishy here.