Unlike apps like LINE, Skype, Messenger, WhatsApp relies on a phone number as a personal identifier. This means that you are pretty much limited to just having WhatsApp on one device (not counting the web/desktop version of the app). This can be a bit troublesome if you own multiple devices that you’d like to receive messages on.
However, the good news is that things could change soon. According to a report from WABetaInfo, it seems that WhatsApp has introduced a hidden feature inside of the Android beta version of the app. Based on this feature, it looks like WhatsApp could be getting ready to allow users to use WhatsApp based on the same number across multiple devices.
This feature is called Linked Devices and it appears to allow users to link multiple devices that uses the same number to a single WhatsApp account. As to why anyone would need such a feature, it could be that some people have multiple phones for work and/or personal, but would still like to receive WhatsApp messages without having to confuse other people with different work/personal numbers.
There is no word on when this feature will be released, but the fact that it made an appearance in the latest beta of the app suggests that it might be launching in the not-so-distant future.