Speed: Thanks to the diminished competition, you don’t have to spend nearly half your life optimizing your site and building links before you can see your site ranking high for long-tail keywords.
Relevance: Since long-tail keywords are more often than not, specific strings of keywords with a several niche terms; the chances of then meeting the exact search needs of users are very high.
Conversion: The fact that search users will find sites targeting long-tail keywords more relevant contribute another point to chalk up in its favor.
Exposure: This is perhaps the least known advantage of targeting long-tail keywords. Using long tail keywords over a period of time will eventually help you rank higher for your head keywords as well. As your site gains authority and builds its trust quotient, the long-tail keywords will help provide enough targeted traffic and also enough ‘exposure’ to your head keywords that your attempt to target them alone won’t prove to be all that disastrous.