Continued from here.
Lord Gusorio pulled up his seat close to the fire, and beckoned the young group of adventurers near. A servant poured mead for the lord, then passed cups to the motley crew gathered to hear the words of the local baron, who was a renowned explorer in his own day.
"You want to explore the Great Dungeon?" the baron asked. "Let me tell you something. I've seen lots of young, brave but foolish folk try it. My companions and I succeeded where they failed. How? By knowing what we were getting ourselves into, that's how."
When a group of adventurers first venture into any dungeon, they're often going in blind. They have no maps, little certain knowledge of the place, and sometimes only the vaguest of goals (fight some monsters and get rich from their treasure being a common one). It never hurts to find out what might be down there before you try to tackle it.
A smart group of players, therefor, will usually spend some time scouting a dungeon (we're assuming a megadungeon environment here, not a one-off site based adventure). It makes sense for the party to go in, find out what's there, then go back and plan how to best tackle those challenges. Parties should explore the unknown slowly, and as stealthily as possible. It's best not to alert or anger any monsters that they aren't prepared to face, especially if they don't know whether those monsters have any treasure or not. Especially in systems where gold=XP, knowing where the treasure is tells you what you need to fight and what you don't.
Scouting also has another advantage. Dungeons tend to have traps, but well-designed dungeons will tend to have multiple ways into or out of any area. If there's a trap blocking access to the next area, careful scouting may reveal a way around it without taking the risk of setting off the trap. This is also true of areas guarded by creatures without any loot.
One area where characters need to weigh their options when scouting is in the choices of armor worn and spells memorized. Those able to wear heavy armors might be tempted to go ahead and wear their plate mail. But wearing leather armor (for the Clerics, Fighters, and Demi-Humans) means the whole party is quieter, and faster. You're not looking to pick up loads of treasure, and you're not looking for a fight. Being faster and less noisy can be a good thing, even if not everyone in the party can Move Silently or Hide in Shadows.
Magic-Users always feel the desire to memorize the powerful low level spells like Sleep and Phantasmal Force. But there are some other good options for scouting as well. Especially, the 2nd level spells Invisibility, Knock, and Locate Object are great for scouting missions. Light is always a good choice for a Magic-User or Cleric to take as well, in case torches or lanterns need to be doused quickly to avoid detection.
Of course, one of the biggest challenges when scouting are wandering monsters. They're unexpected, they rarely have treasure, and the more time you spend in the dungeon, the more likely you are to encounter them. And a party that's equipped to scout effectively may not be best equipped to deal with them. For that reason, scouting missions should usually be fairly quick affairs. Go in, check out some new terrain, map it, make any notes or observations you can, and get out. Especially if there's a wandering monster encounter that can't be avoided, after it's over it's likely time to leave.
I remember reading somewhere about how Rob Kuntz would play his Fighter Robilar when he had solo sessions with Gary Gygax. Robilar would enter Castle Greyhawk, and explore silently as possible. He would never open any doors if he could avoid it, always listened at corners or used a mirror, and tried to see what was there to be seen. Then, armed with whatever information he'd picked up on those solo treks, he'd come back later with a party to deal with any of the threats he'd gotten hints of on those trips.
There are benefits to scouting, to be sure.