Who needs this? Anyone creating an email to send from Hubspot.
The goal? Preventing emails from being caught in spam filters just because a word or phrase you'd like to use is something spammers also typically use.
The value of this would be 1) save time searching the list in the above article when writing the Subject line, 2) increased deliverability and all the goodness that brings.
How is this not a built in feature. We accidentally used "you have been selected" in terms and conditions on an email and Microsoft marked us as a spam confidence level 5. It killed us for 4 weeks while I fought with Microsoft support to update us. Note, you should be SCL = -1, 0, or 1. Anything above that is going to the other tab, and 5 or above is going to junk.