There is no use for them. Everything a Reader or Writer does should be implemented in FeatureReaders and FeatureWriters.
Iβve heard this a few times, but it does seem a little extreme.
I personallyΒ appreciate the cleanliness of having Reader and Writer parameters available in the Navigator rather than just being lumped in with all the other transformers. If FeatureReaders and FeatureWriters were separate in the Navigator...well I might be jumping the fence sooner rather than later.
Also, Iβm not sure about other Smallworld users but I have experienced a few issues using a FeatureReader to read from Smallworld where a standard Reader is fine.