My comments are germain to UA domestic only --
First, most fares allow only 5 segments each way (4 transfers). If you try to push extra segments, it will most likely increase the fare. I occasionally find T fares on Travelocity which have no transfer restrictions which means only your endurance, creativity,(being careful to follow the legal routings) fare and schedule availability become limiting factors. I just call Travelocity and had a "live" agent book the trip. Have not yet had Travelocity do a "forced overnight" on these itns yet.
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JerseyJoe