Hello,
‘Compress document data’ compress only non summary data regarding documentation (f.x. attachments)
I’ve db with images that may be viewed from web.
So will option ‘Compress document data’ increase time of loading images?
Hope my question is clear 
Subject: it depends
This option compresses the non-summary buffer fields like the Body, but NOT the attachments. If the images are not attachments (they are embedded) then it will need to continually compress/decompress thus causing server performance issues. If the imgs are attached then they will not be touched since this compression does not affect atts.