A more serious answer, the 1st Edition DMG had everything you needed to run the rules, tons of stuff you never thought you'd need, and (imho) was written a heck of a lot better than the 2nd Edition; better in, I like the style more, and I think it has more detail. Aging tables, disease table, the barebones stats of every creature from the Monster Manual. All sorts of random encounter tables, including city encounters (of which harlots is a subtable of). The hireling section is wonderful, along with the sage, and I'm now considering seeing how easily I can port it over to my 3E games.
I think the major advantage it had was, there was nothing before it. Gary was creating it from whole cloth, and to make sure everything that was needed was included, he put in everything including the kitchen sink. I'm sure there are parts which I never used, but it's nice to know they're there.