[Rd] What is callGeneric used for?

[Seth Falcon]

I've recently come across two pieces of code using calls to
callGeneric() inside the definition of a method.

In both cases, it appears to me that the callGeneric call could be
replaced with a "real" call to the generic, say foo(x) instead of
callGeneric(x) inside method foo.

My understanding from the docs is that when called with arguments, it
is just like calling the actual generic.  Clear enough, but what does
this provide that just calling the actual generic doesn't?

Similarly, when would one want to make the recursive call that results
from calling callGeneric with no args? 

Thanks,

+ seth