Answer: Google Keyword Planner was created to find keywords for Google ads. It will likely not produce very good keyword suggestions for SEO or content marketing purposes. Google Keyword Planner often hides good long tail keywords. To find long tail keywords for SEO, you can use Keyword Planner alternatives such as Google Trends, Google Suggest or Keyword Tool.
Update: I’ve now been using Long Tail Pro for 5+ years. There are now many different keyword research tools and lots of people prefer some of the newer tools. Admittedly – Long Tail Pro had some hiccups and went through some rough times as they transitioned ownership and introduced the newer cloud version. But – all of the bugs and kinks have been worked out and Long Tail Pro is now better than ever! I’m happy and proud to be able to continue to use and promote Long Tail Pro as my keyword research tool of choice.
What I really like about them is extensive detail including the keyword difficulty. Ahrefs uses clickstream data to also show how many clicks you will get from the search engine. This is very useful after knowledge graph integration, as many keywords may have huge traffic but they hardly get any clicks from the search engine. Reason being, they get answers directly from the Google search result. Example of one such query is: “birthdate of any celebrity”
The limit on manual keywords could be higher. I personally wish we could input 10,000 keywords at a time, instead of 200. However, I understand the costs that Long Tail Pro has to maintain each time a new manual keyword is input. Not a deal breaker, I just wish the limit was higher. (To be fair, I don't think most keyword tools have a bulk manual option at all).