As previously indicated, Lassie uses libraries in several situations. The list below outlines the five places Lassie uses libraries:
Required, minimum of one
This library (or set of libraries) is loaded once at the beginning of the game. A game's graphics library must include all player-character artwork, inventory items, and interface elements used throughout the entire game. All included media must be MovieClips. This library (or libraries) may contain common art assets that are used throughout the game by various rooms as well; however, consider the "common libraries" tactic (outlined below) before overloading you main game library with room-specific artwork.
Optional, no minimum
This library (or set of libraries) is loaded once at the beginning of the game. Sound libraries are kept isolated from graphics libraries so that their loading can be skipped if the player disables game sound. A game's main sound libraries must include all sound effects and character voice that applies to the game as a whole, including inventory responses, default dialogue, and global conversations. The sound library may only include sound media.
Suggested, minimum of one per room
While room graphics could technically be accessed from the game graphics libraries, that would place massive overhead in the initial game load. Instead, it's suggested to create an individual library for each separate room that will load in before the room's first viewing. Loaded libraries will remain in memory until specifically told to unload, so a room will not require loading after it has been displayed once.
Optional, though suggested for each room if you implement sound
Again, sound media should be isolated from graphical media in separate libraries so that sound loading can be skipped if the player disables it. Also, while a room can pull sound from the game sound libraries, it is (again) suggested to create a separate sound library for each room that contains all of the room's voice responses and sound effects.
Suggested general practice
This is not a specific library type like the others listed above... rather, this is just a concept of practicality. When you have common elements that are used in multiple rooms (though not used frequently enough to merit be loaded as part of the game as a whole), just place the elements in a single library that is set to load in multiple rooms. The assets will be loaded the first time they are needed, then will remain loaded into memory for all other instances where they are needed. That's more mileage with less loading.