That's only half of the argument. The other half being that, after having text in there (say, in the edit form of a CRUD app), your user no longer remembers what that field was supposed to represent to begin with.

Probably browser-specific, but some browsers will show the placeholder or label with a hover, as well.

But hovering to see the label is not intuitive at all

Requiring users to hover to determine the context is a horrible UX. Tooltips/popup descriptions should only be used to provide additional information that isn't required.

It's not? The world of computers is filled with hovering for descriptions and details.

It is but an input field is not really an element you would hover for more info. If additional info for the user is required, some question mark icon next to field does the job well because it yells 'hey! something might be confusing or not so obvious'.

I might be an exception but can't recall a case when I would hover input field.

Yeah but that doesn't make it a good idea.

You can't really hover with your finger on an iPhone.

You can set the title attribute to the same as the placeholder.