Let's say you want to send out a message to all of your friends. Normally, you'd have to put all of the recipients into one giant group thread to do this. But when people started responding to your message, everyone in the group would get a notification, so your friends would probably be annoyed that you started the group thread in the first place. Luckily, if you're using WhatsApp, this isn't an issue.
When WhatsApp first came out in 2010, it quickly gained notoriety as a great way to meet new people all over the world thanks to group chats, which allow multiple admins for each group that can all add participants from their own contacts lists.
Getting cool new features before everyone else is just plain fun. To be on the bleeding edge can require a lot of effort at times, since the fastest way to get an update is to find it as soon as it leaks, then get to work on sideloading the new version. Luckily, there's an easier way to get the latest features on your favorite apps, with WhatsApp being no exception.