1) I get a lot more eye contacts with the students this way versus using the blackboard, because I always face the students and never face the blackboard.
2) Beyond streaming the screen, there exist software that records and share what was displayed in previous slides. Students watching the video can then very easily (alt+tab) access another window where they can scroll to check previous slides. OneNote lets you do this for instance by sharing a notebook; the students can either access the notebook on a webpage (sluggish) or on their own OneNote app on a tablet. I typically have 1 notebook for each course and the notes taken during class are updated almost instantly (few seconds). Sadly OneNote has drawbacks: importing a PDF rasterizes it and the result is blurry/pixelated, and the latency for updating the notebook online is few seconds, so not good enough for online streaming.
3) Webex or similar conference software lets each participant send a video stream or a screen sharing stream. I intend to try this setup in the next few weeks: (a) me sharing a selfie video stream (b) me sharing my iPad screen where I write or annotate slides in OneNote, (c) the OneNote online notebook that students have access to in another window with all previously annotated slides, (d) hopefully the students streaming a selfie video of themselves to get visual feedback in the Webex meeting.