Creating a new site from scratch and have it listed among the top results for the content you are targeting takes a monumental effort. There is virtually a zero barrier entry for creation of content on the web and that is the boon and the bane of content on the web.

Hence many content creators seek to address the readers and the search bots (the programs that scourge your web pages and the messengers that get your content to the search engines) separately so that they can find a short-cut to the top of the charts. This separation of content is known as cloaking since you are essentially hiding the actual data from the crawlers.

This technique is what actually brings the whole concept of algorithms and its inability to match human capability into picture. Perhaps search relevancy could be considered a solved problem when cloaking would not make any difference at all.

The definition of cloaking at Wikipedia:

Cloaking is a black hat search engine optimization (SEO) technique in which the content presented to the search engine spider is different from that presented to the users' browser. This is done by delivering content based on the IP addresses or the User-Agent http header of the user requesting the page. When a user is identified as a search engine spider, a server-side script delivers a different version of the web page, one that contains content not present on the visible page. The purpose of cloaking is to deceive search engines so they display the page when it would not otherwise be displayed.

Then there are the other benign forms when it makes sense to want to present different content to different users. This is what has got into a debate in the SEO space with Bad Cloaking Vs Good Link Cleaning.

Overall, it makes sense to weigh in the factors for the purpose of cloaking. if it is to target users alone, then there is nothing to keep you from gaining traction.