The bundling bias is a concept studied primarily by Gourville and Soman in the early 2000's. It explains the fact that we are less likely to get full value from a bundle than from individually purchased items. As a result, we often receive less net utility from bundles, even though they tend to be slightly less expensive than individually purchased items. This occurs because the value of bundled items become associated, so we feel less of a desire to receive benefit commensurate with the cost of each item. We are then willing to forgo some consumption of some items that we would otherwise take.
A commonly cited example of bundling bias stems from an experiment by Gourville and Soman, which found that people who buy a four-day ski pass are less likely to ski all four days than people who buy four one-day ski passes. Because each ski pass was an individual purchase decision, we are more averse to wasting one day than we would be if we had bought all four days at the same time, despite the equal value.