WhatsApp Web was launched by WhatsApp Inc to allow users to chat on WhatsApp from PCs.
The service is really helpful, especially when you work on a PC most of the time, and looking at the mobile screen every time is difficult.
However, the only problem with the service is that its requires the phone to be connected to the internet for syncing and sending messages.
So, the service cannot be used independently, without a mobile phone.
Otherwise, it is really helpful.:)