Peeves' function in the story

[Sam Brown]

No: HPFGUIDX 5528

> Do you think he'll ever get a more crucial role?

I'm convinced that Peeves will have a crucial role in the upcoming 
books based on the information in PS/SS: He's only scared/able to be 
controlled br the Bloody Baron, the Slytherin ghost.

WHY?!

I've got no idea how or why, but I'm sure that JKR wouldn't have told 
us this if it wasn't an important point for a later book. Or maybe it 
was just a meaningless plot device so that Harry could escape from 
Peeves by telling Peeves that he's the Bloody Baron ;) But I doubt it.

--> Sam