> Visa applicants can often be located in the US
Since 9/11, one cannot apply for a US visa if they’re in US. In the context of US immigration, “visa” grants entry, “status” grants stay. If you’re in US, and need to change “status” to a different category (business/leisure, student, etc), you have two primary choices: (1) apply for “change of status” in US, or (2) leave US, apply for a new “visa” in the new category, and enter US using that new “visa”.