still not understanding FROM NAMED

[Bob DuCharme]

I understand the various examples in the SPARQL spec that use FROM 
NAMED, but I still don't completely understand what the FROM NAMED part 
does, especially compared with FROM <http://some/uri>.

http://www.w3.org/TR/2010/WD-sparql11-query-20101014/#namedGraphs says 
"A query can supply IRIs for the named graphs in the RDF Dataset using 
the FROM NAMED clause." If they're named graphs, don't they already have 
IRIs as names? What is FROM NAMED adding here?

thanks,

Bob