Maybe they wanted to send messages from one hilltop to another, where there was no aqueduct. Also the system described may be low bandwidth but it's also low latency. Would be useful to relay messages of a security/defense nature.
Could not much the same effect have been achieved by pulling on a piece of string?
You'd have to make a very long piece of string and avoid it snagging, getting cut, or breaking under it's own weight. Also along that distance there's going to be a lot of slack in the system so you'd have to take that up too.