What are mobile agents? "A mobile agent is a process that can transport its state from one environment to another, with its data intact, and be capable of performing appropriately in the new environment", source: Wikipedia.
Why Mobile Agents .. or how to deal with Data Gravity The phrase "with its data" most likely refers to the agent's state data (and not all types of data), since one of the nicest properties of mobile agents is that they can move to where potentially huge amounts of data is. By plotting the curve "data gravity" - i.e. a rough estimate of how long time it takes to empty/fill/process a hard drive over a network connection - hard disk size divided by (typical) ethernet network speed over the last 20 years - the motivation for moving code to data (and not vice versa) is clearly increasing, making mobile agents a potentially interesting approach.
disclaimer: this posting (and all others on this blog) only represents my personal views.