There are a number of general principles that support the use of a progress tracker:
1- Visibility of system status - One of the 10 usability heuristics of Don Norman.
By using a progress tracker, you inform the user on the number of steps in a complex process and where they're up to.
2- Completion or closure principle in psychology: simply getting that ...
OP could have added a picture to illustrate the context of use of progress bar. In this answer, I will assume it's the kind that indicates which checkout step the user is at, and each checkout step is on a different page instead of the same page.
Progress bars are good for breaking down a long, complex form into shorter, digestible sections. E.g. a ...
In today's reality, many processes are limited to the minimum amount of interaction.
The progress bar function is to show progress or signal at what stage the task is being performed.
If the task is short or easy, it isn't required to create something that indicates its state.
If you consider Shopping-cart as first step of process - I think it's ...