Another feature is that they are, like Unix filters, fundamentally incremental, so multiple processing steps are interleaved and both input and output can stream directly to/from disk/network.  When doing pre-press in the early 90ies (file sizes >> memory sizes) this was a useful feature, and it is still helpful today, see for example the first part of my UIKonf talk:

More recently, the fact that filters are dataflow-oriented and therefore don’t care much about the control flow has made them useful in implementing asynchronous processing pipelines  Think “FRP” just simpler, more readable and faster.  The Microsoft To-Do network stack is implemented using this.

With all the references to Unix P/F, it is probably no surprise that this also subsumes Unix I/O, just with the advantage of an OO hierarchy of shareable behavior.  Oh, and also the interesting feature of subsuming both filters and (output) streams, so ‘stdout’ in Objective-Smalltalk is one of these, a ByteStream that knows how to serialize objects and output them to some target that expects bytes.  And in ‘stsh’ it’s a slight variant of MPWByteStream that is more helpful to a human interacting.