I just had checked for DeepPrime XD’s development times …
The pic from my Nikon D750 was taken at 12.800 ISO when photographing musicans in a dark club w/ mediocre stage lighting. – As @Egregius said, DP XD smooths the out-of-focus parts. That is, when your focus is perfect on the subject you almost get a kind of 3D effect – well, you don’t really but it seems as if the unsharp part is even further away / more out-of-focus → checked at 100% … which means, DP XD can help w/ really high ISO’s and / or heavy crop.
The second pic was taken by another user w/ ILCE-1 at 200 ISO – so definitely no noise! But wait – he had taken an animal with a long lens in good light and the fur was really sharp. Again at 100%, the sharp hairs had gotten just a touch of local contrast and seemed to stand in front of the bokeh parts.
(used DP XD at standard settings – didn’t play around)
I think, DeepPrime XD is a specialized tool and can be quite useful. But if it’s a ‘must’? – Check yourself.