cursor vs. for _row in select...

Can somebody help me to appreciate the difference between returning a
setof record with cursor or with for _row in select ... as in

http://people.planetpostgresql.org/xzilla/index.php?/archives/149-out-parameter-sql-plpgsql-examples.html

Once I use and define cursors read only, no scroll, insensitive (that
should give enough information to use the cursor as a standard query)
I see there is an interesting advantage over for _row in select: you
don't have to specify the output type.

Is there any hidden penalty using cursor vs. for _row in select?

What's the meaning of:
"which can be used to retrieve a small number of rows at a time out
of a larger query".

--
Ivan Sergio Borgonovo
http://www.webthatworks.it