I've got a system that has in excess of 2,000,000 PDF files store in external containers. Each also has a JPG and PNG version stored alongside them.
Attached are two version of one of those PNG files. The original clocking in at 411kb, the compressed file at 41kb.
Let's do some math based on these numbers:
2,000,000 PNG files at 411 kb each =
822,000,000 kb or 822 GB
Now for the compressed PNG files:
2,000,000 PNG files at 41 kb each =
82,000,000 kb or 82 GB
Don't get too crazy with my quick math, that's not the point. FileMaker is using ~10x the storage space needed for PNG thumbnails. I didn't bother compressing the JPG files that also sit alongside the PDF.