Though I wrote this in 2008 I still feel it applies today.http://elearningstuff.net/2008/10/28/forcing-windows-open/
Forcing new windows breaks all web usability guidelines and creates problems for users and importantly affects accessibility issues. International user accessibility guidelines recommend against the “new
When a new window opens in front of the old one a novice user is likely to think that the “back” button associated with the new window will take them back where they were before, and doesn’t know what to do when it won’t, this can be just as annoying as closing the whole window.
Confident users can cope with the forced new window, new users can not.
Similarly a disabled learner, using a head pointer or other assistance device, won’t be able to simply click on the back button to return if the code has forced a new window to open.