If Google has trouble crawling as much as it wants to crawl due to technical reasons, then splitting the load across subdomains or domains makes sense.
Sometimes this makes sense for any kind of static content regardless of Google's crawling; many sites have static content CDNs.
For most sites, this isn't needed. Plus, it won't push Google to crawl more, and more crawling doesn't mean better ranking.
I'm not sure what you mean with "prioritization queue"; this is really more of a technical measure.
Collection
[
|
...
]