Carrying devices across a border gives the Nation State Actors both physical access to your machine
and a legal basis to mess with it - either by searching the device for secrets or by installing malware onto it. Some countries are better at this than others. I wouldn't bother doing this if I was just going from, say, the US to Canada[0]. However, China is notorious for messing with any Android[1] phones that cross their borders. Depending on what countries your company trades with, this policy might make sense.
In contrast, bulk shipments of imported devices are not usually tampered with in the same way[2]. Some countries do have similar restrictions on data import, but they can't mess with or spy on that data because you actually have end-to-end encryption in that case.
[0] I have heard reports of immigration officers demanding device passwords in such a case, but it's rare. If you're really paranoid, enough to want to do this when crossing US borders, I should point out that you should never live within 100 miles of them. Anything 100 miles or closer to a US border gives the US government power to demand your papers; furthermore, the people in border control treat this as a blank check to search for anything they want.
https://www.aclu.org/other/constitution-100-mile-border-zone
[1] I have yet to hear reports of iPhone users getting their phones searched.
[2] Yes I know "Tailored Access Operations" exist, but this usually involves shipping intercepts, not someone buying a device in a store.