Description: User profiles extends existing User preference feature. It gives two profiles to save User Preference. Default profile is global and all users can access to that profile, Custom profile is unique to each user. So each developer could have own Custom profile, while clients could use Default profile slot.
Add elements layout bring option to pick more Oxygen native (Classic view) or Compact view which was only option until 0.9.7 P1.
Fullscreen is new, now it is not real fullscreen but it can mimic Fullscreen pretty close by toggling open/close both panels.
Margin/ Padding Layout was in prototype with earlier Oxygen 4.0, now it is made for RC1 and will give you options to have bigger inputs in classic and column view so you could easier work with CSS Vars and CSS function.
Live server had some case when it would open blank page instead of fronted. For users which does not use it yet, it will show fronted, reload it on save and remove WP Admin bar to mimic incognito.