What is data marshaling and why to use data marshalling?

Marshalling is the process of converting a data field, or an entire set of related structures, into a serialized string that can be sent in a message. To marshall a binary number, one might convert it to hexadecimal digit string, if the message format must be text. If the message will carry binary data, the binary number might be converted into 4 little-endian normalized binary bytes and sent that way. Pointers are harder; one often has to convert them into an abstract reference (e.g., a "node number") that is independent of the actual memory locations.

Please go through below link for more info:

http://www.codeproject.com/Articles/66245/Marshaling-with-Csharp-Chapter-1-Introducing-Marsh.aspx