WAIT FOR NO_THROW option could use some documentation

[Peter Eisentraut]

I don't find any documentation for the WAIT FOR NO_THROW option other 
than a few short sentences in the man page about what it does 
technically.  But I don't find anything about why one would want to use 
it (or not).  I suspect this option was added with some particular 
client control flow in mind, but I think this needs to be explained 
somewhere.