If anything, this is an aid to type-checking. Since MyModule.foo takes only things of type t, the type-checker's job is extremely easy and it will help you a lot more in cases when your program is incomplete.

So often when using C#-style fluent APIs I find that I'm completely on my own and have to turn a half-written line into something syntactically correct before Intellisense gives me anything useful. Using an F#-style MyModule.foo, the compiler can tell me everything.