One important intuition about gzip vs snappy is that gzip isn’t generally parallelizable, while snappy is. If your Hadoop cluster is storing enormous files this shows up very quickly in read performance.
Also, generic CSV is not parallelizable anyway, because it allows you to have (quoted) newlines inside fields and then there is really now way to split it on newlines because you never know if you're on beginning or row or in the middle.
So parallel reading of CSVs is more of a optimization for specific CSVs that you know don't have newlines inside fields.