We have only had one experience using a washer/drier combo...while on holidays in the Atacama Desert.. as the apartment had Samsung washer/dryer combo.
Based on this experience, we possibly wouldn't ever buy one. The main reason is the wash and drying cycle took forever...over 5 hours for both the wash and dry cycles (adding another 3-4 hours for the second half load to be dried). Unfortunately we were unable to air dry our washing as the accommodation didn't have facilities to do so. Being on holidays, we had saved up our washing so that we could do the 4 washes during our two day stay (the total washing and drying time of the 4 washes was around 30+ hours) . This meant that we had to wake up during the night to empty, dry and reload the washing machine. Not very convenient when travelling.
We wish we could have air dried the washing as the water use, plumbing noise was noticeable, seemed very high (we were concerned as we were staying in one of the driest deserts in the world and air drying sort of made sense).
We also thought the drying of the clothes was not as good as a standard heated air dryer. Even after the 8+ hour cycle to wash and dry the whole load, the dried clothes didn't feel fully dry.
However, we may consider buying one in the following, possibly extreme, circumstances...
We moved to a location where air drying was not possible (e.g. very small high rise apartment and/or in the humid and wet tropics/very cold and damp winters) and the laundry at the new location had insufficient room for both a drier and washing machine.
Otherwise, we wouldn't buy one.