When you buy a Chromebook, it usually comes with a two year upgrade of an extra 100GB on your Google account. What I didn't know, was if you could use the promotion again after the two years ended.
For example, I signed up for a free preview of YouTube Red a while back. When the preview was over, I happened to have a Chromecast and there was a promotion for a free month of YouTube Red for Chromecast owners. Unfortunately, I couldn't sign up for that, because I was no longer considered a "new" subscriber.
In 2014, I received a chromebook that had a bonus 1TB upgrade for Google Drive for two years. I gave it a try and the two years ran out very recently. Before it ran out, I bought a new chromebook. I'll skip the story of why I did this. What matters is this: It also had a bonus 100GB on Google Drive for two years. So when my two years of the 1TB upgrade ran out, I went to the Chromebook Goodies website from the new chromebook to see if I could redeem the offer. At worst, it would only be for new users, like the YouTube Red promotion mentioned above.
Fortunately, I was able to redeem the offer. It seems that Google doesn't care if you're a new user or an existing one -- only that you bought a chromebook.
So if you're the kind of person who would pay $2 each month for the 100GB of extra storage, then this is like an extra $48 off the cost of the chromebook every two years. I've seen decent chromebooks for as little as $200, so this can be a significant fraction of the cost. Even some of the nicer chromebooks are in the $300-$400 range, which would make this a 12% - 16% discount.
Side note #1: Keep an eye open for a "security checkup" deal with Google in February. In February 2015 and 2016, they offered an extra 2GB of storage for anyone who did this. I did it both times and I now have 19GB of free space in my account, in addition to the 100GB promotion from my chromebook. (Yes, a total of 119GB of storage for things I was going to do anyway.) The security checkup was a series of questions that you should probably check on anyway, so I highly recommend doing this if they offer it again in February of 2017.
Side note #2: If you have an old G Suite account from when they were free (back when it was just called "Google Apps" and they gave you 100 free accounts), this promotion will work. I'm using it with my account, which I registered in 2008.