Generally I will sometimes block guests from this site solely to try to shake off some of the Chinese search engine spiders that seem to latch on and won't let go. Sometimes i have had to actually reboot the server to shake them off. But this will last only a few days, at most. I believe that most of the guests logged as viewing this site are quite likely search engine spiders, which can sometimes be quite a burden on the server. Some are necessary, of course, but hundreds of them at a time? Especially those originating from countries notorious for being spam sources?
When I go to a new site and find that I am blocked from viewing anything as a guest, I back on out and don't plan to visit them again. It just strikes me as being real user unfriendly, so to heck with them. I lived a long time before finding them, and will live the rest of my life just fine without them, too. Heck, I've even stumbled on sites that block only their classifieds section from casual viewers.
I guess every admin has their own ideas of how to best run their site. Certainly not all of them are going to be successful with their ideas. Lord knows I tried a lot of things along the way with this site. And I'm still not sure I've got this one right yet.....