Newcomers to Google+ have been blocking strangers who add them to circles just because they don't understand the principle of Circles. Blocking in this case is quite unnecessary:
On Google+ anyone can add anyone in their circles and start following the posts.
Those who follow you on the Plus don't see anything you post to your circles, only your Public posts or the posts to Extended circles in some cases...
Blocking is quite extreme and there are concequences.