FOR WHATEVER REASON, you might not want people to know you’re online.
Maybe you want to check other messages without someone knowing you’re checking them, or maybe you’ve received a message from someone who isn’t in your contacts, and would rather them not knowing you’re online.
Whatever your reason, changing this is pretty simple. On both iOS and Android, go into WhatsApp itself and go to Settings > Account > Privacy.
Here you will see three different entries: Last Seen, Profile photo and Status. Tapping on any of these allows you to change it from everyone seeing it to just your contacts or nobody.
Remember that if you decide to turn off last seen entirely, you can’t see when anyone else was last online.
The other two options you have include blocked, which prevents specific people from being able to message or call you, and read receipts which is effectively the blue ticks you see when you open up a new message.
Much like the last seen option, turning this off means that you can’t see if the other person has read your message either.
Of course, you could always just keep them on and respond to messages when they come in, but where’s the fun in that?