Lot of blogs, either using plugins or a little custom PHP code publish articles that are intended purely for their subscribers, with the content appearing only in their RSS feeds, or in emails generated from the RSS Feed.
Lets look at this from a number of points of logic
- Best “public” content – if you are reserving your best content for subscribers, then you might be limiting the number of subscribers you receive. I look on this as a little different to “premium content” that might be served within a membership site or private RSS feed / email list – there is a different level of commitment.
- RSS Syndication – your RSS content isn’t only available in feed readers, it can also appear on multiple syndication sites for easy reading without subscription
- Scrapers and Search – Your subscriber only content is going to appear on RSS scraper sites, possibly without even a link back to you, but not on your own site – how logical is that?
If the content really is intended just for your subscribers, lock it away in a membership area and require registration to access it, even if you subsequently serve it though some kind of password protected RSS Feed using Http authentication or customer unique feeds.
You can even have premium content indexed, but blocked by a pay wall.
I understand there are psychological benefits advertising that subscribers to your feed gain access to content not available on the main blog, but realistically the methods people use are shooting themselves in the foot.