Immigration is sharp on allowing "visa free" for tourist visits only.
Arrival in CGK: Asked for destination and hotel name as well as purpose of visit.
Departure in DPS on 6th day: No questions asked
Arrival in back in DPS three days later: Asked where I was coming from, how long I would stay. After I replied that the stay is only one night, he asked which hotel, where the hotel was located and whether I'm not visiting someone or was on transit.
Departure the next day in DPS: Same questions again after the official saw we spent only one night in Indonesia. What hotel and if we were really tourists.
We were indeed "real tourists" - but for anybody transiting or visiting somebody, better be careful or have some "details" ready when arriving and departing.