Yeah, the uses for the send/return modules go deeper than just an insert point for stompboxes. For one thing, it's basically an "unfixed" effects processor, as the actual processing done depends on what you choose to drop into the insert, and this can be as simple as a fuzzbox or as complex as an entire pedalboard. And then there's their uses as extra mono-outs or external signal inputs.
One thing I need to try is using something like this to admit a no-input system's signal into a modular for final manipulation. My AE system has a couple of their 4I/O modules (like these, but with four "soft" I/Os instead of the dedicated input and output), so it should be a good candidate for this.
-- Lugia
Cool. As I forgot to say, it's also a great way to bring in an external synth or even a guitar, say, where the level is too low otherwise for modular. All in all, a useful little gizmo!