I have seen paths that will generate upwards of 10 promises and then put them together at the end. In theory, this shouldn't be a problem and the code was readable enough. Reasoning about all of the different ways backpressure can happen was not as easy.

Compared to knowing that you have a set of queues that ultimately feed into other queues. It is much clearer to reason about the throughput of individual queues and take that into consideration when designing new queues in the system.

It is basically like someone throwing a ton of outlets on a wire going through a room. I mean, yes. You can do that. Often won't even cause issues. However, for large enough systems, you ultimately need to know what the load on that circuit will be and it is not acceptable to put yet another plug extender there.