There is a particular kind of Bali trip that starts with a one-way flight and no fixed ending. You book a guesthouse in Canggu for a week, plan a few days in Ubud, and leave the rest open. Maybe you will head to Lombok, maybe you will stay longer, or maybe you will move on to Malaysia. That flexibility is part of the appeal.
But Indonesia's Visa on Arrival arrangements include a return or onward ticket requirement. If you are using that entry route, it pays to organize your departure plan before boarding your flight to Denpasar.
You do not need to build a rigid six-month itinerary. You need to understand the entry category you are using, the period it gives you, and what your onward flight document should show.