channel of channel is a normal pattern, although it more commonly looks like a channel of struct vals, and the struct type has a field that's a channel. it's lets you send requests that are completed, whose values can be awaited on out of order, to avoid head of line blocking. something like `type request struct { params, reply chan response }`, where you send those requests on a channel, they get dispatched to some worker, and then the worker does the work and puts the result on the reply chan. But two is as high as I've ever found useful, I don't think I've ever seen a use case for a chan chan chan.