Methods are nice but suffer from the fact that adding a custom method to a new object is more involved and dangerous than just creating a new function. However, "f(g(h(x)))" is not very readable (at least for English speakers) since while we read left to right, the invocation order is right to left. "x | h | g | f" is arguably more readable since the evaluation order follows reading order (plus you don't have to deal with so many parenthesis).

I want to reemphasize though that introducing a variable is often better practice and that the pipe operator only makes sense when there is no suitable variable name.

There's also a "hierarchy" thing at play. With "f(g(h(x)))", x is "inside" h which is "inside" g which is "inside" f. With "x | h | g | f" all are on the same level. For me at least, it's easier to imagine your data "flow" through functions when they are on the same level. It sound a bit weird when I put it that way, but I don't think I'm alone in feeling that. Fluent interfaces are considered easy to read, and help flatten the code. Same thing with promise chaining compared to the callback > of doom.

But it's not the case for the majority of libraries, including many of the builtin types.

A pipeline operator is generic and can be used everywhere, without requiring the API to be built around chaining. This can often lead to much nicer, more readable code.

I think this is something you only start to really appreciate once you've used it a bit, like in Elixir or F#.

Obviously this is much more natural in a functional language, where everything is immutable anyway.