When a report comes to me and says they finished early, I quiz them on what they have done. If it's too good to be true, it usually is.
Did the report get their task straight? I want to make sure that they did not misunderstand their task.
Did they execute the task on the basis of unwarranted, short-cut assumptions?
What methodology did they use, and does this methodology makes sense? if they use a method that no one thought of and it is effective and efficient, I want the repo to write me about it and cc the rest of the team.
Did they adequately QA their work?
Assuming that they passed my review with flying colors, I'll have them back up other members of my team who could use some assistance. Or do some self-study to prep for an upcoming project, do some documentation work, investigate a new technology, etc. There is always something to do.