ZBrushCentral

ZTL file size vs hide mesh

Hi,
When I save my work example is 80 mb, after I hide some parts and I wonder when I save again my work is 230 mb. Then I unhide these parts and save and my work again 80 mb.
Why?

Do you have subdivisions?

Yes, I have subdivison. I tried this with many different files, same thing: Hide mesh=increase file size


Hide mesh why increase file size?