The trigger object is extremely useful anytime that you want to force multiple output messages based on a single input.
Trigger has an outlet for every argument you type in and each outlet has an output type defined by the associated argument. Arguments can define a variable that passes messages of the correct type unaltered while converting those that do not match, or they can be constant values. Whenever trigger receives any message in its inlet, it outputs the associated message for each outlet in right to left order.
For more information on using variable types and their conversions, see the help patch or reference file.
In Max Basic Tutorial 5: Message Order and Debugging trigger is used to force the order of output of messages. It also demonstrates how trigger converts numerical inputs of different types.
Max Basic Tutorial 6: Simple Math in Max uses the trigger object to force calculations when passing values into cold inlets.
Jitter Tutorial 31: Rendering Destinations demonstrates a common use of the trigger object in OpenGL environments to control rendering order. This is used in many patches that deal with OpenGL, where you need to erase the previous frame before drawing the next. Note the use of the "l" argument to pass the jit_matrix <matrixname> list.
You can abbreviate the word trigger and simply use "t".
This simple patch takes the idea of calculating the delta between two input values that is shown in the help file and applies it to a matrix:
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