The short answer to what appears to be the actual question is that in the [tag:United-States], the required effort provides a defense to complying with a subpoena when it is "unduly burdensome." [Fed.R.Civ.P. 45(d)(3)(A)(iv)][1].

This is a flexible standard that means different things in different contexts. Imagine, for instance, that complying with a subpoena would cost $1 million. If you sent the subpoena in connection with a small-claims lawsuit over a $200 bill from your plumber, the recipient would have a good case that it's unduly burdensome. 

But if the subpoena came from the government as it sought to disrupt and prosecute a terrorist network on the verge of launching a domestic attack, that argument is going to be a lot weaker.


  [1]: https://casetext.com/statute/united-states-code/title-28-appendix/federal-rules-of-civil-procedure/title-vi-trials/rule-45-subpoena