Shift+B is Build Ram Preview. It’s a quick method of Previewing your work AND Is limited by the amount of BUILD RAM PREVIEW you’ve set aside in Preferences. Being a RAM option it’s volatile and WILL disappear if your Timeline is altered. Now, if you wish to have less volatile Previews then use SHIFT+M, and this is PreRendering. Then there is the further option to Render-Out for ongoing editing?
I’ve tried all these methods and select to use them based on what exactly I need AT THAT TIME.
So, what are you trying to achieve:
Volatile/Ephemeral Previews? This will give a quick and dirty view of your work thus far. It can range from a few seconds, to, if you have the RAM to TENS of Seconds or even minutes! 🤩
More Stable Previews? PreRenders > SHIFT+M
Previews that you’re needing to use for editing? Render-Out or intermediary renders.
I think you’ve confused Build RAM Previewing with PreRenders.