> Any links to famous cases, or is it all secret squirrel that we can't be trusted to know about?

It is fairly common for indictments of persons not already in custody to be sealed initially if there may be issues with effecting arrest, and sometimes for other reasons (e.g., to avoid compromising parallel investigations). The grand jury process is intended to enforce probable cause requirements, not to provide notice to the accused so that they might better flee arrest.

Several of the indictments by the Special Counsel’s office, for some famous examples, were originally sealed.

They are very common, quite a few felony arrests start sealed to prevent the alleged criminal from fleeing. Or on foreign individuals so they will travel to somewhere they can be grabbed.