docdownloadid is related to a new feature we built for downloading attachments as a zip. Multiple records can reference the same attachment and we want to download it only once. By having the docdownloadid=1 header, that adds in the docdownloadid in the doclinks child object for each record that has the attachment. This generates unique strings for this specific session for security purposes for our request to download the file.
After we have downloaded the record data (without the file contents), provided the maximo.mobile.attachments.autoDownload system property is enabled and the user has not disabled it in their application (in the Settings->Offline data), we then make a request to download these files. This is done using an API call like this:
/maximo/oslc/doczip?ids=bnB6&maxfs=5120000&mimetype=pdf,zip,txt,doc,docx,dwg,gif,csv,xls,xlsx,ppt,xml,xsl,bmp,html,png,pptx,cfr,jpeg,mp4,mov,odt,ods,odp,jpg,jpeg,rtf,wmv,wm,wma
The ids= would be a comma separated list from the docdownloadid.
I'll be honest, I don't know what optimize does though or if it's even used.