it's more of a thing if applying online, for e-Visa.
With the e-Visa portal, you can only upload 1 document relating to your employment, so you need to compile several documents into one and it's helpful to explain those by means of a covering letter.
For an in-person application, you can simply explain it in-person.
In that case, I'm not sure how you can truly verify your current location.
Some folks in this group believe that the embassies/consulates can check your immigration status in Thailand. If that's the case, at least they can verify that you're out of the country...
That's one part of it, but some others mention including a photo of their passport, showing the entry stamp to the country, where the application is being made.
If, for the sake of argument, one booked a hotel in Hanoi and used that booking as evidence, whilst they're actually applying from Thailand, it might work. What if they ask for more evidence, such as a photo of the entry stamp to Vietnam?
I'm not saying it's likely, but it's certainly possible. With the e-visa process, if your application is rejected, you lose the fee.