Ah, old-style monster books, with pages and pages of random encounter tables in the back.
As a GM, you'd sit there and roll up an encounter, and then decide you didn't like that one and roll again. And again. And again. Until you got the one you thought was cool and interesting to start with.
Obi-Wan: So is there anything I can do while the others are enjoying the sights?
GM: Sure, let me crack open this shiny new Giant Sand Creatures book. There's an encounter table in the back. I'll roll up something for you to fight. <roll>
GM: 32... let's see... everything from 01 to 80 is a...
GM: ... sandstorm?
Obi-Wan: I run back inside the ship! Guards! Inside, there's a sandstorm coming!
GM: This is lame... just a sec...
Obi-Wan: Captain Olié! Batten down the hatches!
GM: There's a really cool monster on page 37...
Obi-Wan: Looks like a big storm. This will affect the town as well.
Qui-Gon: It will?! I draw my sword!
Jar Jar: Wesa in a market! Put that away!
Qui-Gon: Oh, right. Thanks.
GM: You can't fight a sandstorm. The sand just gets in everywhere, inside clothes, armour, destroying electronics—
R2-D2: Oh man. That's me screwed.
Obi-Wan: Oh, really? I hadn't considered that...