Here’s the interesting aspect of this conversation – the client is an intelligent, educated man, reasonably technologically adept who has been using computers since the 1980s and has been on the internet for over 10 years. And yet – he thinks this way?
Here’s what Jakob Nielsen has to say:
Opening up new browser windows is like a vacuum cleaner sales person who starts a visit by emptying an ash tray on the customer's carpet. Don't pollute my screen with any more windows, thanks (particularly since current operating systems have miserable window management).
Designers open new browser windows on the theory that it keeps users on their site. But even disregarding the user-hostile message implied in taking over the user's machine, the strategy is self-defeating since it disables the Back button which is the normal way users return to previous sites. Users often don't notice that a new window has opened, especially if they are using a small monitor where the windows are maximized to fill up the screen. So a user who tries to return to the origin will be confused by a grayed out Back button.
Links that don't behave as expected undermine users' understanding of their own system. A link should be a simple hypertext reference that replaces the current page with new content. Users hate unwarranted pop-up windows. When they want the destination to appear in a new page, they can use their browser's "open in new window" command — assuming, of course, that the link is not a piece of code that interferes with the browser’s standard behavior.
The only exception to this would be when linking to .pdfs or .xls files or some sort of non-html file.
Designers and site owners should not think that it is their business to decide when users should have a new window. It's their computer, their decision to make. Furthermore the whole point of hyperlinking is the seemless linking from one point to the next. Opening up another window breaks the connection between sites.
Another reason, less important simply because opening new windows is a bad idea, but very important in the coming few years is the increasing use of cellphones with small screens. Mobile devices don't always support multiple windows and even when they do the user experience is quite limited in keeping track of the open windows.