In the United States Supreme Court, a person who wants to file an amicus curiae (friend of the court) brief must either have consent of the parties or make a motion for permission to the Court.  SCOTUS regulars regularly consent to nearly all amicus briefs because everybody knows there is nothing gained by refusing.  The Court nearly always grants the motions.

Eugene Volokh has done some empirical research on what "everybody knows," and this time "everybody" is right.  After excluding a few oddballs, he concludes:

So, as best I can tell the Court has never -- not once -- in the last 14 years refused a normal, professionally prepared, rules-compliant amicus brief (one that was filed in time, by a nondisbarred lawyer independent of any party, and with normal, substantive legal argument). If you are asked for consent to the filing of an amicus brief in your Supreme Court case, there is basically no upside to refusing, and some modest downside. Just say yes.