Hang on to your ticket!
When I travelled to London Bridge recently, using a Bat & Ball to London Terminals ticket, I was surprised when the ticket barrier retained the ticket. Previously, these tickets were returned in case the holder required to continue to either Cannon Street, Waterloo East, Charing Cross or Blackfriars. I queried this with the barrier staff, and they advised me that you now need to ask them to let you through the barriers if you wish to continue your journey later.
You’ll also need to go through the manned barriers if you need to keep your ticket – for instance if you need to claim Delay-Repay!
With all the platforms now connected at London Bridge I’d presumed it was because there was no reason to exit (aside from needing a cash machine or the WCs)