Types are checked during unpickling. Most Alice values can be pickled. There are some semantic implications and necessary restrictions, though. They can be freely pickled and unpickled. After putting a functional object in a pickle and reextracting it it is indistinguishable from the original object.
Stateful values do contain objects like references or arrays.
Stateful data can also be pickled freely. Sharing between stateful object is maintained inside a pickle, though. Sited objects are connected to a parent process. They refer to certain resources that are not available outside the process. An example is the input stream of an open file.