One critical point to note is legality. In practice it matters whether a spy agency needs to go in covertly (via technology or human means) or whether a random

One critical point to note is legality. In practice it matters whether a spy agency needs to go in covertly (via technology or human means) or whether a random police station in rural Illinois can just send a quick mail and get data of German citizens immediately. In fact, in many cases it's beneficial for states to share data with other countries, but they want that to happen on the basis of laws, cooperation and in a two way fashion. Unilateral laws such as the CLOUD act are a problem.