First off, writing f3(f2(f1(x))) is painful - keeping track of parentheses. If you want to insert a function in the middle of the chain you have some bookkeeping to do.

Second, that's all good and well if all you want to do is map. But what if you need combinations of map and filter as well? You're suddenly dealing with nested comprehensions, which few people like.

In F#, it'll still be:

    iter |> f1 |> f2 |> f3 |> f4

Here's an example from real code I wrote:

    graph
    |> Map.filter isSubSetFunc
    |> Map.filter doesNotContainFunc
    |> Map.values
    |> Set.ofSeq

This would not be fun to write in List Comprehensions, but you could manage (only two list comprehensions). Now here's other code:

    graph
    |> removeTerminalExerciseNodes
    |> Map.filter isEmpty
    |> Map.keys
    |> Seq.map LookUpFunc
    |> Seq.map RemoveTrivialNodes
    |> Seq.sortBy GetLength
    |> Seq.rev
    |> Seq.toList

BTW, some of the named functions above are defined with their own chain of maps and filters.