Blizzard is currently working on the next major update for
Overwatch which the developer says will require a complete re-installation of the game client. Over on the
forums, a Blizzard customer support rep offered a brief explanation as to why you will be required to completely reinstall the game.
The next major patch will have some pretty fundamental changes to the game client. The number of back-end changes we’re putting in is substantial enough that we can’t just patch over the current content efficiently. As a result, when the next patch comes out, the client will fully reinstall itself to handle these changes. We know that this isn’t ideal for people on metered connections, so hopefully this announcement helps you prepare for this coming update.
In a response to Kotaku's initial report, Blizzard provided a bit more context for the upcoming update, which the developer called a "remaster" patch. According to Blizzard (via Kotaku), the update is "intended to improve load times, optimize memory for 'constrained systems,' reduce hard drive space used by the PS4 version, fix bugs 'across many maps,' and make changes to data formats to 'support future content.'"
The update will require both PC and console players to re-download the game. Currently, there's no release date or time for when the update will arrive. Thankfully, Overwatch isn't a particularly huge game to begin with, checking in at just around 13GB. It's possible that this update could even shrink the size of the game which is awesome for those pressed for hard drive space.