When we talk about timeliness as an element of good communication, we are seeking to answer the question of when do we communication? The "when" answers how often or with what frequency communication should occur.
It's a critical question because too much communication increases the "noise" factor and naturally causes recipients to tune out. When people get in the habit of ignoring communication, a valuable service is effectively lost -- or at least degraded -- and it is hard to make a come-back.
In the absence of other input, many organizations settle for some sort of recurring communication combined with lots of random communications in between.
The noise factor in such cases is unknown, but is rarely in the Goldilocks zone of "just right".
A trigger in process-speak is an event that creates the need to execute a process. It is the defined start of a process, which, along with inputs and activities, will cause a process to create one or more outputs.
This is a handy way to look at answer the question of when to communicate. A communication trigger defines an event or circumstance that creates a need to disseminate valuable information to recipients.
The event or circumstance can be anything and is likely vary a lot depending upon your business, your products, your services, and your recipients.
Additionally, there can be any number of events or circumstances that trigger the need to communicate. However, the main point is that each event or circumstance is identifiable and unique.
This makes the "when" a non-issue. You communicate when a trigger has occurred, no more and no less. That's not to say that triggers will never need to change. They will most certainly come and go over time. This is where having a communication plan really shines, helping you to maintain the triggers and all of the other moving parts required for good communication.
It may be instructive to provide examples of triggers for communication as these will clearly illustrate what a trigger is and how it helps control how often communication should occur.
Hopefully this demonstrates how triggers are defined and how they establish when communication occurs.