A customer determines value by comparing one thing to another. There is more than one type of comparison a customer can make in any given instance. Customers may value something more highly when they make one kind of comparison than when they make a different kind of comparison. Making a comparison is key for a customer to determine the attributed value the customer gives to a product.
When faced with side by side comparisons people begin to place importance on attributes that do not really matter when it comes to the real value of a product. Often these attributes would not play a role in customer decision making, but faced with side by side comparisons these attributes suddenly seem important to the customer. Thus a customer may end up purchasing a product based on attributes they deem "better" even if they didn't know what the additional benefits offer. Often it is highly likely that before the customer was confronted with side by side comparisons most of these benefits did not matter and would not have played a role in the end purchase of the product.
You may notice that retailers put out large displays of similar products so that people will begin to compare the attributes of these products. People will begin to consider the possible attributes rather than considering whether the product is really better than the similar product. Likewise they will consider these possible attributes when comparing them to the similar product that they ALREADY own. Most of the attributes don't vary drastically, but from a customer who is intent on buying a new product all that is seen is that this product has this attribute and the other product does not have this attribute.
People focus on the attributes that the marketer put in front of them without considering whether this product is really that much better than the one they already own. Thus, if a marketer can place a certain emphasis on attributes that seem important (even though they may not be) they will more likely than not entice the customer into buying a produce even if they may not need or want it.
More often than not a customer will spend more money on attributes that really don't matter (they may not even know the benefits of these attributes). But hey, at least he will be able to brag to his neighbor that his camera has a better flash output than theirs!