There are not many sites that offer full RSS feeds. The very idea of using only a brief part of the full article is still the most popular way of feeding. However, the situation is changing. The user of full length article feed is growing slow popularity in the market. So far, only some of the news sites are providing full news RSS to their subscribers. There is no use of full RSS feeds in blog or content based sites and there is no chance that marketing or business sites will adapt this concept in near future.
The introduction of RSS held the idea of drawing visitors to websites. So at the initial state, the RSS feeds were all about sending plain text which usually contains the magnetic part of an article following a direct link to the article. If the reader finds the partial article interesting, he clicks the link to read the full article which increases the traffic to that website. Later, decorating feeds was introduced. Now you can add image or you can style the fonts and colors in your feeds. These features make the feeds more attractive. Even the site owners can style their own feeds by using a third party feed service provider like Feeds API.
For last few years, the concept of using full RSS feed was developed among the dedicated readers who do not want to waste time in visiting the whole site and later find out that it does not have anything useful for them. So when the reader gets the full article right in his feeds, he does not need to go through the website which is time consuming. The reader can decide right on the spot whether the article is useful for him or not. If the article has quality and can grow interest of the reader, there is a good chance that he will visit the website to find out if there is more articles similar to that. If the quality of the article is very low, the reader will eventually lose his interest and will unsubscribe his membership from that website. So the possibility of losing traffic for sites with full RSS feeds is very minimal.