Am quite new to Pega as wel as testing. Been looking into AUT on pega 7.1.6 last couple of days.
Advantages of the AUT in pega seem similar to any other unit test, being able to perform automated regressiontesting. So you can identify functionality that has been impacted unintentionally.
The flow markers are basically snapshots from where you can continue testing a flow. This enables you to resume testing form a certain point in a case without having to supply all inputs again. Testing flows are actually testing entire cases becouse you can only create testcases on startflows.