I just have the free version right now so I don't know all that the pro one can do. But even the free version has A LOT of tools you can use, I haven't even figured them all out yet. But one that I have used is their Content Optimizer. You can take a new or existing content piece of yours, and compare it to one of your competitor's pieces on a similar topic, and see where you might be lacking based on the keywords that are used in each piece.
The Google Keyword Planner used to be great it's now frustrating to use.... and almost impossible to get in to without setting up your first ad. Big shame google big shame. I would love to share more info about your tool over on my website [link removed by moderator] for my local business clients - have you got something you can send over for me to add to the site?
This isn’t the only tool that mines Google Autocomplete. There’s also KeywordTool.io, but this tool restricts results to ~700 keywords (more are available for “pro” members). Infinite Suggest is another alternative, but despite the name, I’ve found that it still doesn’t find anywhere near the number of keywords that Keyword Shitter finds. And there are tons of other Google Autocomplete miners too. Just Google “google auto suggest tool” for more. There’s also this tool from SEOChat which mines autocomplete suggestions from Google, Bing, Amazon, and YouTube.