Reactions can help you gather signal from your team on what they feel is important. I like forcing a first or second choice (versus just vote for anything) since it forces everyone to make the hard cuts.
When product questions, get a quick read from the working group on what their initial leanings are to see which questions are controversial and worth diving deeper into
If everyone is on the same page already, you may be able to cancel that meeting!
Speaking of meetings, reactions can help make them more inclusive. We drop a "dory" at the bottom of every proposal so the best questions rise to the top instead of the loudest person in the room dominating the conversation
When you have a pre-read it's pretty important to know if folks have read it or if they need more time during the meeting to read. A done reading reaction takes the guesswork out of it.