At North Texas RPGCon this year, one of the things I did was a first playtesting run for Cyclopean Deeps Chapter 9: Hidden Worlds of Jupiter Kwan. This particular bit of the Cyclopean Deeps has been an open question for a long time with me. It is a very complex map with lots of possible locations (at least 300, I'd estimate) and multiple possibilities for several things in each of the areas.
When you're approaching an adventure that contains locations with multiple nested possibilities, there are basically three ways to do it. You can key all the locations, you can create tables to generate the various internal possibilities on the fly, or you can pre-generate a huge number of locations using those tables.
Option 1 (Key ALL the rooms!) had to be discarded immediately, if for no other reason that when you've got 300 keyed locations, your map looks like it's nothing but numbers. You can barely tell which numbers go with which location.
Option 2 (Multiple Tables) was what I playtested. Each time the adventurers entered an area, I rolled on the several tables required to generate the area. I immediately discovered that it wasn't going to work. There was way too much page-flipping and fast reading going on as I tried to assemble a description of what the characters could see. So, I am now in the process of creating a large number of pre-generated locations. There is still some die-rolling required, but this will cut it in half and minimize the need to flip pages around.
Normally I consider pre-generated locations to be the worst of both worlds: by numbering everything you can get well-crafted descriptions that are highly unique, and by creating a full set of tables you can get an even larger number of descriptions, although they will of necessity be a bit less well-crafted than if they were all written out straight.
What are the Characteristics of an Adventure that Works Best with Pre-generated Random Locations?
However, Chapter 9 of Cyclopean Deeps has a particular set of characteristics that happen to work best with pre-generated locations: the movement is fast from place to place (in real time), the areas involve several different possible components, and there are many of these locations.