From the example on their home page I realize there is be a number of parts that may benefit from being produced this way.

It's however NOT a replacement for most composite parts made "the old way" with layers upon layers or with braided composite structures.

The user rm2014 made an interesting comment about inserting fibre into filament in the RepRap Forum five weeks ago: http://forums.reprap.org/read.php?1,302667