On that date, you'll be able to link your Destiny 2 accounts between multiple platforms and access your characters on all of them.
For Destiny 2, developer Bungie wanted to incorporate cross-saves for character progression, but the idea was blocked by Sony.
On a blog post, Bungie has officially stated that August 21 will be the day cross-save becomes available. Most of that differential is likely accounted for by the content added with the free-to-play New Light edition of the game, and by Bungie's estimates, Shadowkeep will slap an additional 60 GB onto that figure. Silver is linked to your characters, so if you have Silver on a different platform or a different set of characters, you won't get to access it.
In case you would like to find out more about the next expansion and armor 2.0, know that on August 14 there will be a live on Twitch in which the new equipment customization system will be explained in detail. The new feature will be enabled for PC, PlayStation 4, and Xbox One.
That doesn't mean your other characters are gone forever, though. A date for this to happen was not announced until yesterday.
In other words, if you plan to play Destiny 2 on an SDD, it may be time to think about how you're going to thin the herd a bit when it comes to games you've got installed when October rolls around.
In more Bungie news, the upcoming expansion, Shadowkeep, was originally slated for a September release, but has since been delayed to October 1. Starting on August 20, however, PC users can start linking their accounts between Battle.net and Steam to make the transition easier.