You know... I don't want to be a conspiracy theorist, but... the media has suddenly stopped talking about Trump's problems with women.
Well the documents were sent in an envelope with the address of Trump Tower.
This leak provides the context for all the other ones. When other tax returns are leaked, either by him or by someone else, showing that he paid no Federal income tax whilst earning a lot of money, then he won't have to explain it (having to explain things always looks bad) because the explanation would have been given in the media today.
That's one reason for him to leak this
It should say something if we're seriously considering that Trump might have leaked potentially damaging info (which this likely is, to a large number of voters) just to push some
other damaging info out of the news cycle.
This reminds me of something Nate Silver talked about recently: there's
so much stuff about Trump that there isn't enough news cycle to cover it all. He quantified this by defining a "mitt" as a unit of shady/questionable/newsworthy stuff about a candidate. 1 mitt was defined as the amount of this clinging to Mitt Romney, a mostly straight-up guy. Obama was also pretty clean, perhaps a little shadier than Romney; say 1.2 mitts. Hillary Clinton, OTOH, has a lot more baggage, probably in the 5 mitt range. But Trump is at least 50 mitts -- which is so far off the scale that it can't all be covered in depth. So he only gets covered at about a level of about 7 or 8 mitts. (This was written a few weeks ago; that number might be higher now.)