Weak, imprecise language makes for bland storytelling. If you’re playing a storytelling game (and we all are), which would you rather encounter:
“A huge group of barbarians is coming toward you dressed in mismatched armor and ragged clothing, some on horses. What do you do?”
“A legion of horribles, hundreds in number, half naked or clad in costumes attic or biblical or wardrobed out of a fevered dream with the skins of animals and silk finery and pieces of uniform still tracked with the blood of prior owners, coats of slain dragoons, frogged and braided cavalry jackets, one in a stovepipe hat and one with an umbrella and one in white stockings and a bloodstained weddingveil and some in headgear of cranefeathers or rawhide helmets that bore the horns of bull or buffalo and one in a pigeontailed coat worn backwards and otherwise naked and one in the armor of a  conquistador, the breastplate and pauldrons deeply dented with old blows of mace or saber done in another country by men whose very bones were dust and many with their braids spliced up with the hair of other beasts until they trailed upon the ground and their horses’ ears and tails worked with bits of brightly colored cloth and one whose horse’s whole head was painted crimson red and all the horsemen’s faces gaudy and grotesque with daubings like a company of mounted clowns, death hilarious, all howling in a barbarous tongue and riding down upon them like a horde from a hell more horrible yet than the brimstone land of  reckoning, screeching and yammering and clothed in smoke like those vaporous beings in regions beyond right knowing where the eye wanders and the lip jerks and drools. What do you do?“1
No, none of us are Cormac McCarthy, and yes, this is probably too much text to speak or read in an actual game session. But both are saying, fundamentally, the same thing. In the first, detail and specificity are elided. There’s a horde of bad guys coming at the party, and that’s it. Any party knows what to do when generic bad guys approach: you attack. The cue given by the GM allows no other reaction: there’s no hook to parley or negotiate; there’s no detail to indicate whether the party is under- or overmatched and consequently convey to the party whether they should scoff, grandstand, deceive, or take to heels. Our games tend to be (over recent years, particularly) designed to encourage the perfect tailoring of challenge to PC ability. The consequence of this is that we have trained our players that in the absence of explicit indication to the contrary, every encounter will be a fair fight.
If you’re always guaranteed a fair fight, you’re likely to get into a lot of fights.
But consider the second. Yes, it’s likely too long to see use in any but the most set-piece of games. But it conveys information, tone, setting. The tone is what draws attention: no one here is run-of-the-mill, and the aggregate is just as interesting as the individual. We know this is a horde of savages.2 There’s a lot of them, many quite distinguishable. The juxtaposition of those in “the skins of animals and silk finery and pieces of uniform” shows us that there’s nothing homogeneous or regimented here. The warrior nonetheless clad in “white stockings and a bloodstained weddingveil” shows us that he cares not about the significance of these items in the culture he is being contrasted against, or does and is wearing them for effect, or doesn’t understand their meaning in a culture beyond their purely functional use as items of clothing. (Let’s ignore what we can guess about how, exactly, this man got a blood-stained wedding veil in the first place.) While the bare paragraph is lengthy, each of the warriors depicted is described–in just a few words per–evocatively enough to be an interesting antagonist by himself.
Here, we get information. The horde is savage. They are “horribles,” great in number and fierce in aspect, armed for war but clad as though they care not for what fate befalls them. Armed for war–massacre and counter-massacre–of the oldest sort. They are fearsome: they wear bits of uniform “still tracked with the blood of prior owner,” armor “deeply dented with old blows of mace or saber,” and they ride down on the PCs “like a horde from a hell more horrible yet.” We get information. You can bet they can be neither greeted nor pacified. You can fight, or flee, and the odds are good you ought to choose the latter.
But most of all, the PCs have knowledge, and can use that knowledge to make realistic choices. There’s no treasure here, only the strong probability of having your blood used to daub crimson to a horse. Maybe the PCs are powerful enough to win, maybe not, depending on your party. Maybe you have previously given them a reason to stand and fight. But here, they know that if they do, they are standing against nothing less than a force of nature, the wrath of an angry god, the collective avatar of all that opposes civilization. Doesn’t that sound like a lot more fun than the first encounter?
1 Cormac McCarthy, Blood Meridian or The Evening Redness in the West (slightly amended).
2 Let us disregard, for the moment, McCarthy’s characterization of the Comanches as barbarous, if for no other reason than that everyone in Blood Meridian is barbarous. It is a book of “ever bloodier and more damnable outrages” (Banville) with a villain who is, “short of Moby Dick, the most monstrous apparition in all of American literature” (Bloom). It is not a light read, but no one is more evocative.