I like how Signal just shows that the person exists as a contact. Whether they're awake or not, or active, or idle is opaque to me and I'm totally fine with that.
One of the reasons for text based chat/messenger apps, going all the way back to the earliest days of IRC, is the benefit in having asynchronous communications. If I absolutely need an immediate answer from someone or a realtime 1:1 conversation on something urgent I'll call them on the phone instead.
In things like facebook messenger I bet that 99% of users never dig into the settings to turn OFF the "show your activity status to other people" option.
For something like a work place communication tools such as Slack I can understand the purpose of setting yourself active or idle manually to indicate whether you're available for messages, or in a different time zone, or whatever. That's a different use case.