In Adobe Campaign Classic, Display progression information is the appropriate action to monitor variables being passed through the workflow. This feature provides insight into the data being processed at each step, which is essential when debugging. Here's how it helps:

Progression Information in Debugging:

This setting allows developers to see the data transitions, including variables passed between activities. By enabling progression tracking, developers can view detailed logs and understand what variables are passed at each stage of the workflow, which is particularly useful in identifying issues within JavaScript activities.

Visualization of Variables:

This action offers an interface to view records and variables directly as they move through the workflow, showing interim data sets. It makes it easier to confirm the correct variables are being passed or identify where unexpected values occur.

Thus, using Display progression information is the optimal choice to observe variable transitions throughout a workflow, aiding in debugging JavaScript and other activities.