Because WhatsApp currently only allows you to link computers to your account, adding support for tablets (or possibly an additional phone) would only make sense.
However, there are some limitations to using linked devices. You can’t, for example, clear or delete chats if you use an iPhone as your primary device. You can’t also send messages with link previews from WhatsApp web, message or call someone using a “very old version” of WhatsApp, or view live locations.
