A common technique for games is to use a combination of triggers and Flow Graphed logic, to force certain events to occur based on what the player is doing or has even done already. This is where you create the experience for the player. A reason why you want to implement scripted events with triggers is to introduce new traps, new gameplay elements, and other situations. If there is a new type of enemy or a very dangerous portion of the level coming up, a scripted event can be used as a powerful design tool that can communicate important information and focus the player.
When working on level's within the CryENGINE SDK, a designer has access to different types of triggers, some of which operate on a proximity basis where they check how far the player is from the center of the trigger, and some which are even simpler, such as checking whether the player enters or exits a certain area.