images used in pdf generation on cloud stored in separate subdomain

I would have expected the images to be with the main site. The only time I recall seeing images (and CSS and static HTML pages) being hosted on different domains or subdomains had to do with some sort of attempt at performance enhancement but it never struck me as worth the effort and I have never seen it repeated.

It could be something as simple as a limitation in the code generating the PDFs. Maybe using one subdomain allows the images to be freely moved around with breaking filepaths and such as the images on a subdomain are (I presume) always in the "root" folder

@Ray - I did a little bit of digging and apparently WordPress uses this to "speed up" site loading. Personally I cannot see it making a discernable difference. The argument is the number of TCP sockets per connection to download things. By using a separate subdomain you double the number of download sockets. Or some such .....

I doubt it would do much for PDFs but I cannot find any other reason. The only advantage I can see it conferring is the reduction in URL length as all images are at the "top" of the path's folder lists.

Interesting... I agree that it would probably not make much difference, given that WP loads so many script files.  All of the WP pages are slow compared to bespoke web sites, but that's just the nature of frameworks.  I'm wondering if there is some other reason -- perhaps licensing the images in a unique way or something like that?

Having static resources served from a CDN allows for more concurrent downloads in the browser and ergo a faster loading website.
Very common, especially in image intensive websites.
If the browser is stuck downloading 100 images from your site then it cannot do anything else til they have finished, by offloading it to a different server it allows your website to continue loading.

@Gary: Yes, good point.  But a CDN in a separate subdomain?  I just haven't seen anybody do that.

I use it all the time for all static stuff like css, js etc, it's not quite a cdn but it is in many ways
Eliminates cookies and allows parallel downloads.

I said different server (though there is an advantage to that as well if it is more local to the visitor), but I should have said different website as mysite.com is not the same as www.mysite.com

I think "mysite.com" probably resolves to a local DNS, and it would be the same local DNS as test.mysite.com, docs.mysite.com. www, etc.  I would refer to these as different sub-domains of the same web site.  Different terminology, but I think we are saying the same thing.

I asked,. He didnt know. Shall i close the question it a dead end

thanks