I was using Movie Studio 17. I loaded a 4K video with a large data-rate, and allowed it to 'adjust' the settings of the project.
Then I made edits, for instance lighting and sharpness. But when resaving the file... It is very small compared to the original file-size:

Length in seconds 29.
Frame width 3840
Frame height 2160
Frame Rate 29.97

Original Data rate: 202687
Edited Data Rate: 23559kbps

Original File size: 743,215kb
Edited File Size: 86,979kb

Audio bit rate slightly went down too, but not significantly.
I looked around for settings, but couldn't find anything relevant. So the resulting video is not just small in size, but the quality is visually impacted.