With the advent of dolls in presents, it has become quite common to possess dolls that are, perhaps, not quite what one would have selected for themselves. At the same time, given their rarity it's kind of a shame to trade them in for dingbats, especially when other people would be interested in said dolls.
Having the ability to trade dolls to other people (in exchange for a doll of theirs) would help this out considerably.
For example, I could trade this doll: "doll168648" a plush doll of Princess Marilynth
to Azula for a doll of Glumki, which would leave us both feeling quite pleased with the situation.