While researching keywords for your website, you will come to know that there are a number of keywords that can be targeted. Most of these keywords will be longer than 2-3 word key phrases. Optimizing a website for one or two word keyword is very difficult but if you target a long term, it will be a relatively easy job.
The keywords that are more descriptive, usually have a low search volume but high conversion ratio. If you combine all your long tail keywords', they will show a reasonable search volume to target and such key phrases are searched by mostly a prospect buyer of your services.
In the figure above, we are targeting the keyword 'shoes'. This keyword has a very high search volume and because of that a very tough competition. You might get noticed for this keyword through an advertising campaign but your website and products listed over it must be very interestingto get user attention.
The second keyword is mens shoes'. In this keyword, we have specified a category men' so we'll only get users who are searching for mens shoes. A low cost and relatively low risk keyword but conversions for this keyword word still remain a question with respect to the website and products listed over it.
Now we move to the very specific users of search engines who are willing to buy and are looking for red Nike mens running shoes'. It is a long keyword but very specific. Competition will be very low or there might be no competition at all for this keyword. Conversion ratio will be high and it will be very easy to optimize a website for this keyword.
Bottom-line; Research keywords properly and never ignore those keywords which have low search volume as they might be the best ones to target and get high conversions.