The border control system is full of these gotchas and opportunities for arbitrary harsh punishments. Just off the top of my head, and a mix of US and UK:
* Be careful saying you are travelling for "business" or "work". The two words mean about the same in everyday use, but at a border check one is perfectly fine and one is a giant no-no.
* You apply for a 30-day visa and are granted a 90-day visa. If you decide to extend your trip to 90 days you can be banned for misrepresentation.
* The whole thing with "intention to immigrate" that is basically policing your internal mental state. It's perfectly fine to travel to America on a non-immigrant visa, decide you like it there and apply for a change of status or a new immigrant visa. Someone who planned to do that from the beginning is violating their visa, but of course it's impossible to prove unless they slip up.
* There are many situations where you are allowed to stay in a country, but if you go on any trip to an other country you will not be let back in. For example if you are waiting for an extension application. Not fun if a parent is suddenly sick in hospital and you want to see them before they die.
* Be careful saying you are travelling for "business" or "work". The two words mean about the same in everyday use, but at a border check one is perfectly fine and one is a giant no-no.
* You apply for a 30-day visa and are granted a 90-day visa. If you decide to extend your trip to 90 days you can be banned for misrepresentation.
* The whole thing with "intention to immigrate" that is basically policing your internal mental state. It's perfectly fine to travel to America on a non-immigrant visa, decide you like it there and apply for a change of status or a new immigrant visa. Someone who planned to do that from the beginning is violating their visa, but of course it's impossible to prove unless they slip up.
* There are many situations where you are allowed to stay in a country, but if you go on any trip to an other country you will not be let back in. For example if you are waiting for an extension application. Not fun if a parent is suddenly sick in hospital and you want to see them before they die.