Monadic IO allows you to reliably sequence IO operations, but the results of those operations are not produced until their results are forced. Here's an example of the problems with this: http://dev.stephendiehl.com/hask/#lazy-io . It's not really a language flaw, but more of a design flaw of the functions in base.

Almost nobody uses lazy IO anymore though. Most IO is done w/ strict IO functions from the bytestring library and often with stream processing libraries like conduit or pipes.