QF and LH have some interesting fares. Interlining works perfectly.
QF sells LH feeders to the FRA flight. LH sells QF segments on the way to Australia.
You can earn your points each program (A* Programs for LH, and 1W Programs for QF).
You can check through the luggage without a problem.
You will be protected in case of a misconnect.
But: You wont't get a BP for your additional segment. I had quite a wired case! A pax booked MUC-SIN on LH and SIN-MEL on QF in one ticket. Her passport was valid for 5 months and she had a valid Visa for Australia.
Problem: SIN needs a Passport to be valid at least 6 Months! The checkin-system did not allow to process a BP for her, as the LH system could only process the BP till SIN. It was quite a hassle! LH in MUC bend all the rules (with the risk beeing fined) to let her on board the flight! On the way back she got a temporary passport in Australia in the embassy!
So be careful with the entry regulations of the airports where you have to connect!!!