It was really nice. With the current linear design I organize desktops by theme (e.g. one for dev, one for research, etc) and with the 10.5/10.6 design I'd use vertical desktops for subcategories — so following the same example, on a single screen setup I might have desktops arranged something like:

   │   Rails Docs/Search   │   Backend Dev  │    Music   │
   ├───────────────────────┼────────────────┼────────────┤
   │   UIKit Docs/Search   │     iOS Dev    │    Chat    │
   ├───────────────────────┼────────────────┼────────────┤
   │  MDN/Web Dev Search   │     Web Dev    │ Email/News │

With this, I quickly develop muscle/spatial memory for where each category "lives" and can navigate there in a flash. It also substantially reduces the need for individual programs like browsers to bear organizational load, so for example suddenly "just" single-tier vertical tabs become sufficient, making browser workspaces and tree style tabs much less necessary.

The added dimension really made things intuitive so you weren't left guessing which vertical had to do with what. One space would give you enough context to know what might be next navigating up/down. It's really a shame how disruptive the change to Mission Control was by removing them.

I tend to organize my spaces by projects and then a dumping ground for "everything else" like general browsing and music.

For projects, unique windows are typically: IDE, Browser(s)

For apps I commonly use across spaces, I assign them to "All Desktops" so they follow me, like iTerm2 and Heynote for keeping notes / task lists even if they cover multiple projects.