First, it records search queries that people have used to find your website and adds those keywords to your keyword list. Keywords may be a result of a paid search in which, for example, you're able to view the extended search phrase of a keyword on which you're broad matching. This is crucial to growing your long tail and increasing your specific keyword phrases, which tend to have lower competition and more appropriate audiences. Keywords may also be a result of an organic search , something pertinent to your website and product which you haven't yet incorporated into your PPC campaign.
Last, it updates the keyword popularity  and keyword relevance  rankings, used by the Workflow tab  to help optimize your time. A weighted average of keyword commonality and visits generated, keyword relevance indicates the importance of each keyword so you can adjust your time and bid amounts accordingly. Keyword relevance also guides your segmentations so they're as optimized as possible.
Properly segmenting keyword groups is a crucial step towards a high Quality Score and one that's easy and efficient from within WordStream. After adding keywords  and visit data to your account, WordStream gets to work evaluating keyword relevance based on visit count and keyword commonality. Use the Workflow  Tab to receive segment suggestions, which are re-evaluated each time you accept or reject a segment suggestion, so you're always looking at the best ones.