Customs officials forcing you to unlock your phone is not just an invasion of privacy - it's a pointless invasion of privacy. Customs agents don't even know where to start in finding data that a user wants hidden. Even if allowed access to personal devices, data is slippery enough that it could be stored in almost anything. Here's yet another example of taking away rights in a way that does nothing to deter actual cr…
I suspect that the people they're trying to catch by doing these searches (pedophiles, illegal workers) are generally too stupid or lazy to bother hiding their data. At least, that seems to be the case when watching Border Security. They do actually catch a lot of people this way.
So you would catch the lazy criminals, and maybe even victims of such act, where things were done on their devices without their knowledge... I've read recently about new kind of software, that encrypts your data without your knowledge and then asks you for money to unlock it - wondering how this would play in courts...