Start some program that shows a progress bar on the console, or other non-interactive refreshing display, and hold down the enter key to see every char it outputs.

Is the output optimal, or does it just refresh the whole line each time?

Optimal example:

joey@darkstar:~/src/concurrent-output>./demo2
Pinwheels!!  -
Dots......!  ...............
             \
                            ...
             |
                               ...
             /
                                  ...
             -
                                     ...

apt-get update is an example of a non-optimal output.