Editing Smart Objects Increasing File Size

I am working in Photoshop CC (on Mac OS) and I have set up a document with 3 Smart Objects shapes that I input different images for to print. Every time I switch out the previous image with a new image in the Smart Object, my overall storage on my hard drive drops. I can't for the life of me figure out why it keeps going down because I am not saving the main parent file. I am simply just switching out the images to print and then closing out the parent file. When I add the new image into the Smart Object and the close the tab it does ask me "Save changes to the Adobe Photoshop document “Image2.psb” before closing?" and I click Yes to pull it into the parent document. So are these psb files being stored somewhere else that is taking up storage? I can't find them anywhere if this is the case. Any help would be much appreciated!