single user prtocal can be only used specifically for one 
type of functionality execution example if u r recording  
web http protocal for client-server based app then if in 
between there are a requirement of sending ftp reponses 
back to server then some times it happens that your reponse 
exactly what u want to send back doesnt go...so better to 
use both http and ftp protocall to record....

This is purely based on the application for an example if 
your application developed by Siebel as a front end and 
back end as Siebel Oracle at that time if we select only 
siebel may not be able to retrieve all the request and 
responses.So we need to select multiple protocol for Siebel 
and Siebel Oracle.