From Google Analytics perspective it makes no difference if you use
_blank or not. Google Analytics will still see 2 pageviews in any case.
If the link goes away from your site then
_blank could even reduce the Bounce Rate, but from a usability point of view not from a technical point of view.
_blank open a new window/tab instead of using the current one when navigating a link. People tend to use it on external links to avoid users leaving their sites. Another use case is for help articles on Web Apps, since the user don't necessarily want to exit the app to look up a help article. All in all there are no general guidelines to where to use it or not. This is up to you. As a user I personally think that too many
_blank links are annoying.