Actually that is all that I use my Summoning Dolls for - mules. I have one carrying a full load of potions so that if I run low, I can summon the doll and transfer more potions to my main character.
Also if you have saved a ton of loot to trade for some YIT charms you can summon all your dolls and load up 4-6 character inventories to have enough items to trade for those ~65000 gold charms.
It would be hard to gain much experience for a summoning doll, since if you move very far the doll vanishes.
