There's not a particular use case for runHscQuickTest.sh that's important. It's really only as a minor time savings to catch reasons runHscTest.sh might fail without having to download the 700 GB of validation_data_hsc.
I will add a descriptive note in the README about having to explicitly set up the cloned repo of ci_hsc if one wants to use runHscQuickTest.sh and a reminder that ci_hsc doesn't install anything into the stack dir.
The current ticket was meant to produce something that could be run, e.g., by SQuaSH. That's the full runHscTest.sh script.