Google have made many interesting product decisions and direction changes over the years and now that we've all come to depend on their raft of free services they're making, in my opinion, potential impactful and disruptive changes.
Google+ has been trying to break ground into the Social space for sometime yet seems to never quite get a foothold and this new change is yet another attempt to extend it's reach. In short, anyone with a Google+ account can email your gmail account even if they don't actually know your email address. Hmmm, this sounds a little spammy to me increasing the chance of of even further unwanted email that we ultimately have to manage in some way or another.
If you're concerned about your time spent on useless things such as managing an ever growing inbox of junk, here's how to turn this off. http://tinyurl.com/ltey3ks
More good reading on the subject can be found here:
A location for inspiration and comment... (but primarily just my point of view)