Perhaps it would be better to ask, how do you expect people to communicate to you those things that would be expressed as reactions?
That is, there is no ack signal.
Unfortunately, I work with humans and technology, both of whom are fallible. As such, reminders and prompts are occasionally required. Being able to tell if a message was received, read, and understood is a very useful signal.
Reactions are an interesting workaround, where people that need to ack a message can just send one, and the client can collapse repeating ones into a number, not bothering anyone.
But, of course, every client needs to know about that for it to work.