First, when I say wandering monsters, what am I talking about? What are wandering monsters, as defined by the games I've played?
“Wandering monsters”are hostile things that traipse around looking for trouble. They might actively patrol a wilderness area or an underground dungeon. They could even pop in from Hell without rhyme or reason!"
- GURPS Dungeon Fantasy 2: Dungeons, p. 20
"Wandering Monster -General term for any encounter not previously keyed by the DM; usually refers to the periodic check for monsters in dungeons."
- AD&D Dungeon Masters Guide, p. 230
In other words, either monsters who are just moving around the dungeon or you just didn't plan for.
GURPS Dungeon Fantasy has rules for checks, and I've used them. The rules are fine. In fact, I've even proposed expanding them so you roll whenever you're in a fight with other monsters, planned or unplanned - aka, dogpiling wandering monsters. Like how this card works in Munchkin:
Wandering monsters can be a lot of fun - and monsters moving around helps deal with PCs who don't. Camping PCs, PCs digging through the floor or steadily bashing down the walls, etc. - wandering monsters come by and attack the PCs and it costs them resources for sitting there.
But sometimes, I just find them annoying. Weak, dumb monsters aren't a terribly big threat to an organized group, or one that's being alert. Strong, dumb monsters aren't in such big supply that they can be filling the hallways.
In D&D-ish games, where only AC and initiative can prevent damage, wandering monsters are a threat. They might get the drop on you and get in a round of attacking, hit, and inflict some damage-cost on you. Or they may survive a round of pounding and equally hurt you before they die. In GURPS, this is much less likely in my experience. Unless it's a serious threat to the life of the party, it often feels like it's just a time-waster for everyone involved. And if it's a serious threat level of a monster, I have to wonder why I didn't place it in my dungeon (more on that below.) Nuisance monsters - spiders, jellies, giant rats, minor patrols of humanoids - aren't powerful enough to be real threat and get beaten easily.
So I'm finding they disrupt play more than they extract a cost for lollygagging in the dungeon.
Of course, getting annoyed with having wandering monsters isn't unique to me. This quote should secure my old-school cred if I decide to forgo the rolls when they're in the way of play:
"For example, the rules call for wandering monsters, but these can be not only irritating - if not deadly - but the appearance of such can actually spoil a game by interfering with an orderly expedition." - AD&D Dungeon Masters Guide, p. 9
Even Gary Gygax acknowledged they could do more harm than good, sometimes.
So what to do?
I have a couple of "wandering monster" tables, but I don't always use them. Instead, I will sometimes roll on my table to see what comes by, and other times I'll just have a nearby creature react to the noise (I mentioned this a while back.) That way, it's a combination of "just out wandering" and "unplanned reaction from nearby enemies."
I think this is more of the tactic I need. Make it a "who do you alert in the neighborhood?" kind of situation.
If I was being more systematic about it - and in the future I might - I could roll my d6 but make the entries like this:
1 - (monster)
2 - (monster)
3 - (monster)
4 - (monster)
5,6 - Nearby creature(s) alerted, comes to investigate.
I could even merge it with the wandering monster roll itself, although it'll skew the percentages a bit. If the chances of an encounter are 9 or less, then an 8 or 9 could be "nearby creature investigates."
But I'm not sure about that, yet.
Still another option is to, say, roll a "wandering monster check" for all the nearby monsters. Basically, an activation roll - do they get motivated to react to the disturbance? In a classic dungeon, they might or might not. Living creatures are living because they aren't dumb enough to go out and look into any disturbance, I figure. Only truly badass monsters can take the risk of leaving their stronghold area and going out looking for a fight just because all that iron-spike tapping is disturbing them.*
So rather than roll them up, I could roll to see if they get activated. In this case, the "dogpiling" rule I linked to above isn't necessary - the separate rolls for each will determine who comes.
Another option is to combine both - some areas, especially wilderness, would use a table.
"The desert is swarming with bands of hostile creatures, and adventurers will encounter them from time to time.
- GURPS Dungeon Fantasy Adventure 1: Mirror of the Fire Demon
In those cases, there is no outside limitation on what could be around the area.
Others would use a mixed table, like the above - everything from "these guys are wandering far and wide from their base in area #11" to "oops, you woke up the minotaur in the room nearby, and he's coming for a looksee."
But all together, I'm still finding myself making less wandering monster checks and more judgment calls - just eyeballing who is nearby and deciding if they're likely to get involved or not.
I like the idea of wandering monsters, and of a resource/danger tax on lingering in places you don't belong, but I'm finding the effect isn't what I wanted. More "time waster fights" than "real danger of harm." Less fun-for-time for everyone, GM and players included.
So I haven't really made up my mind which way I want to roll things and run things, going forward.
* This is the "once shot a man for snoring too loud" thing. See John Wesley Hardin; also in GURPS Who's Who 2.