There doesn’t seem to be anything online about CastChecked.
Can someone explain for future readers?
Probably an internal function to check if cast function fails or succeeds
All you have to do is
AMyClass* cl = Cast<AMyClass>(Other);
and unreal does the asserts behind your back 
CastChecked is exactly what it says, it’s a checked cast. It’s the equivalent of:
ptrA = Cast< type >( ptrB );
check( ptrA != nullptr );
It’s not an internal function but you do have to be pretty sure that the cast is going to succeed.
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Yep basically in another word.
Use Cast() if nullptrs and incorrect types in your results are an expected behaviour.
UseCastChecked() if you want to throw an error immediately if the cast fails.
This is not entirely accurate. There is an enum parameter that you can pass to CastChecked that allows for nullptr inputs to not trip the check. It’s common for the case of “if this pointer is valid, it should always be X, but it’s okay if it’s not valid to start”.