Rewarding Exploration
The party is investigating an old house with a lot of fireplaces in it. Only one fireplace has any treasure inside (behind a loose brick). It would suck if the players investigated one fireplace, found nothing, and were discouraged from investigating any others. So instead of putting treasure inside only one of the fireplaces, the treasure now has no fixed location. It's inside whichever fireplace the party happens to investigate first.
This does not actually reward exploration.
It's not really a reward to be handed treasure through no actual effort. Exploration is rewarded when players make a choice and make a deduction that there may be something of value in the fireplaces.
If the players decide not to search additional fireplaces, it is their choice to not do so and not finding the treasure is the consequence of their choice.
A better way to do this is to put the treasure in one fireplace and then add a clue or feature that may logically lead to the players wanting to investigate it. For example, describe a small pile of loose stone (debris from moving the brick) or describe one brick to be slightly uneven, or some other feature unique to this fireplace that may suggest further inspection.
Advancing the Plot
The party doesn't know it, but there's an important document inside the dungeon that will turn their world upside down and send them on their next adventure. Since finding the document is imperative to the plot, giving it a fixed location wouldn't necessarily be the best idea -- the party might never find it. So instead, the document is wherever the players happen to look. Do they search an old desk? Papers. Do they find a treasure chest? Papers. Do they search someone's body? Papers. It might seem ham-fisted, but it's better than having to nudge the party in the right direction later.
If the document is integral to there being an adventure, I would just give the players the document at the beginning. I don't see the point of going through the motions.
Imparting Information
The party is struggling through a dungeon that ends with a fireball-casting wizard. You want the players to know what they're up against so they can prepare accordingly (by preparing absorb elements, boosting their Dex saves, acquiring fire resistance, etc.). There's a clue in part of the dungeon -- maybe a large scorch mark that any Arcana-proficient character can recognize as the aftermath of a fireball spell. But if you want the party to have this information, then why leave it up to chance? Drop it into any room that the party happens to visit.
Telegraphing threats is a good tool in the DM arsenal. However, I wouldn't just drop it into any room the party happens to visit. I would instead think about where this wizard lairs, and put the marks in a logical location. The room should be somewhere that can allow the players to be able to make an educated guess as far as where the wizard may be located. It should give them the ability to decide to avoid the area or go wizard hunting.
So, what would you call this sort of thing? Is it fudging? And what do you think of it as a DMing tool? Is it wrong? Is it good? Do you ever do it yourself, or is it against your DMing code? Let me know!
The main point to this is that if you want to just throw stuff in non-fixed locations, be careful to do so such that it does not invalidate player choices or eliminate consequences.
I recommend checking out this blog. It has a fantastic description and analysis of your proposals. Personally, I consider this blog to be required reading for anyone who wants to DM.
You think you're saving effort. You're not. You think you're making things more 'fun' for the players, but really, you're ruining their fu...
hackslashmaster.blogspot.com
Blog has gotten pretty big. . . I'm reorganizing the index to make it more useful (Updated 8/22/14) If you like the blog, subscribe to t...
hackslashmaster.blogspot.com