Good afternoon.
Reveal is a valuable tool, but it DOES cause problems that the user must be aware of going in.
Problem 1: Reveal, by preventing the "discovery" of your magma well/pipe, prevents you from building magma forges/smelters/etc.
Problem 2: If you reveal a map containing an underground river/pool, you will never get the spores necessary to have tower caps and such grow underground.
Problem 3: HFS. If you know what I'm talking about, great. If not, take a peek at the wiki. The important thing to know is that reveal breaks HFS too.
Problem 4: Revealing the map provides more "known" resources for your moody dwarves to demand. They'll pine for that ONE faint yellow diamond down 16 levels below ground.
Problems 1, 2 and 3 are caused by reveal bypassing the "discovery" mechanism. Interestingly, if you have a visible magma source, it starts "discovered" and the bit that allows magma constructions gets set properly at embark. But revealing does NOT do so. That's why the "enable magma buildings" tool was created.
The good news is, you can work around this quite easily.
Purist method: Copy your savegame to a different slot, and reveal THAT game, not your primary. From there, you can easily determine where you have to dig to discover your magma, river, iron, whatever. As long as you never reveal your ACTIVE game, you can't mess anything up.
Drifted snow method: Start your game. Copy your save, and reveal the copy just enough to find all your key underground resources, ie magma, rivers, etc. THEN, dig in your active game until you've discovered all of these resources. This will properly set all the necessary bits, and then you're free to reveal your primary game if you like. Just make sure you discover everything relevant first - INCLUDING HFS.
It's a useful tool as long as you understand the consequences of using it. However, once revealed, there is no way (that I've ever seen) of UN-revealing a map, short of reverting to a pre-reveal savegame.
Rochndil, who has been known to drift now and then...