I'm assuming 3.5 edition. If this thread is using 3.0 rules, ignore this post.
Hiding is not a "move-equivalent" action ("move-equivalent actions no longer exist, but that's the the point of this post.) Hiding is typically a non-action taken as part of a move.
Meta-game thinking:
Suppose a human you see, located 150' away just beyond a 3' wall, uses bluff to create a diversion (standard action). When you turn back to where that person was, you can no longer see him.
With your previous assumption that hiding is a move action, it would be obvious that the human is still right there behind the wall (he just ducked below the wall while your attention was diverted.)
However, since hiding is actually part of a move action, he could be up to half his movement rate away from where you previously saw him (or up to his full movement away if he took a penalty on the hide check.)
Character thinking:
"Well, he cannot be too far from where I just saw him. I think I'll just center my sunburst (80' radius) where I last saw him and hope he's within the area."