Interfaces for reading email, for me, are all about getting through lots of messages quickly.
Having only the subjects makes reading email much easier. I am not even tempted to look at the message. I just hit the "Edit" button and tab through the email marking stuff to be deleted.
It remind me of the "good old days" of Elm!
Please take note of the word "read". The interface is horrible for replying to email. It encourages bad grammar/short replies.
Oh well... it just means I reply to less email :)