Terrain

Current practise in most games is to use a mix of procedural and manual world (i.e. terrain or map) design:

Manual (i.e. pre-made) World Design

For example, The Elder Scrolls V: Skyrim -

Procedural Terrain Generation

For example, Minecraft -

Advantages of Procedural Terrain Gen:

• The world can be infinite (in theory), but either way it can be much larger than any manually designed game world
• The world (or at least parts of it) can be regenerated for each game, potentially increasing replay value, since the player will always have something new to discover
• Once created, sometimes changes to maps can be made quicker using procedurally generated methods, e.g. decreasing the incidence of a particular biome by changing a single threshold number, as opposed to manually removing the excess biome areas from a pre-made map

Disadvantages of Procedural Terrain Gen:

• Players can get "stuck" in a location (e.g. surrounded by lava and cut off with no way out) if a world is poorly generated
• The randomness could make enforcing difficulty settings highly variable - e.g. everything could generate in one spot, making life very easy for a player (or a group of players) regardless of "difficulty" setting
• If previously visited areas are regenerated during gameplay, there can be a lack of familiarity, which is an important element of exploration
• If the generation is poor in dungeons or maze type areas, then multiple instances of these areas generated with different paths can still "feel the same" or "repetitive"
• Finer details, landmarks or monuments may be more difficult to place in a purely procedurally generated world

Other Considerations with Procedural Terrain Gen:

• Giving help to players can be difficult - there can be no definitive "walkthrough" in a procedurally generated world (not really a problem for sandbox or non-linear games)
• Replicating issues and testing for bugs in a procedurally generated world can sometimes take much longer to find and fix (given the randomness and thus difficulty to recreate the issues) then it would've taken to make the world / map manually
• Procedurally generated maps can be more technical in design and require more technical skill than manual map design (e.g. creating a waterfall)