Synchronized output is merely implementing the feature as inspired by iTerm2 synchronized output,
except that it's not using the rare DCS but rather the well known SM ? and RM ?. iTerm2 has now also adopted to use the new syntax instead of using DCS.
When rendering the screen of the terminal, the Emulator usually iterates through each visible grid cell and renders its current state. With applications updating the screen a at higher frequency this can cause tearing.
This mode attempts to mitigate that.