what is advantage & disadvantage of creation of multiple & single irule?

What does the iRule(s) do? are they very specific to each application/virtual server?

In my option, too, one iRule is better than many... but if the iRule is :

if we are in application 1: cmd1 cmd2 ... if application 2: cmd3 cmd4 ...

then maybe separate iRules is cleaner and easier to maintain.