I prefer to have a choice. You could have a compiler that doesn't run it you haven't eaten a balanced breakfast either. Haskell's type system is designed around type inference (of the Hindley-Milner kind), if it can infer the type I'd like to have the option to let it do so.

It's certainly good practise to write out your types, and often your editor can do it for you, but there are tons of little places where it's a waste.