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It's only my opinion, but most named-variety mulberries are probably offered as grafted specimens because it's easier to propagate large numbers of grafted trees than it is to produce even a fraction of that number by air layering.

In zone 10...I don't know if there are any advantages or disadvantages, but in zones colder than 7/8, it's advantageous to have Pakistan on its own roots, or to bury the graft union below soil level...so that if(when) it freezes back to the ground, it can resprout.

Dr. AJ Bullard, the long-time NAFEX mulberry expert, said that the lowest recorded temperature in Islamabad, where it originated, was 28F.
I had Pakistan for a number of years - planted, on Dr. Bullard's recommendation, with the graft below grade. It froze back to the ground three years in a row, and those were not particularly severe winters; would resprout and grow 8-10 ft, but never fruited here.
I see folks purporting to grow and fruit Pakistan in zones more northerly than my southern KY location, but always wonder...do they really have 'Pakistan'?

Thanks for the explanation lucky_p. Pakistan Mulberries are also called Himalayan Mulberries. If you call them that, they sound more cold hardy.

Of the several Pakistan trees here, all but one have similar r/s-to-Pak. trunk girths after years of growth. The one with the thinner Pak. trunk is about 30% thinner, and this tree is just as old as the others. It seems that the r/s definitely dwarfed it's grafted scion, and that might be good for having a shorter canopy to pick fruit from. No problems with that idea. BUT...., when this early March after all the m/b trees had already come out of dormancy and were sporting tons of new leaves and new fruit, a surprise freeze happened with 100% ice coating on everything that rain could reach and 23 degrees to go with it. The thicker trees with thicker branches lost all the leaves/fruit like the dwarfed tree, but there was a WHOLE LOT more dead branches on the dwarfed tree. Even though they were the same age and had the same r/s size. Lesson learned: Thickerer is betterer when a late freeze blasts through after the trees come out of dormancy...... If I was just starting out with "young" Pak. trees in a place that can get freezes, Each late Fall I would surround the tree with a 6 foot tall circle of fence at least 4 foot wide and just fill the whole thing with dry leaves. In Spring when I was relatively sure that freezes were no longer a risk, I would lift the circle fence and push the dry leaves aside for the branches/trunk to start growing out. I would not get rid of the leaves for another "while" until there was even less chance of a later freeze....just in case the leaves need to be put back inside the fence. Afterwards, the leaves can be placed around the tree for mulch, since they will shrink downward over time. The fence goes on vacation until next Winter. Over the years the lower 6 foot of the tree will get thicker and more cold hardy. And hopefully bust out with new leaves and new fruit on the branches within the 6 foot-high area after the leaf covering comes off each Spring.