There’re both merits and demerits explained below -
*Demerits:*
1) **It doesn’t provide a very good privacy.** It doesn’t have a feature for different privacy levels for different people. For example, you may want to let some people see your last seen while not for some. But you can either turn it on or off for everyone.
2) **WhatsApp doesn’t allow you to use same account on two different devices.** In case you have two phones, you can’t switch same account on both phones.
3) **WhatsApp doesn’t allow you to send big files**. It has a size limit to send a file.
4) The latest policy says that some of information / stats of your WhatsApp account will be shared by Facebook in order to make improvements. Many of the courts worldwide doesn’t consider it to be an honest idea.
5) If you don’t want to be a part of a group in WhatsApp, you can leave it. But someone can add you back. You can leave again. He can add again. It can go on recursively. **There’s no feature on WhatsApp not to allow to add back in a group.*
6) There’s **no feature of Video call** on WhatsApp.
Merits:
1) It is automatically synchronized with your address book. You don’t have to add contacts individually.
2) It is fast, smooth and efficient and very easy to us. It takes very less amount of data to send messages.
3) **Messages are end-to-end encrypted** which means no other third-party can see what you have sent to your contact.
4) You can **make a voice call** with your buddies.
5) You can **broadcast a message** in case you have to send a same message to multiple contacts. The person’s will receive message individually.
6) You can use your WhatsApp with your computer through **WhatsApp web**. But for that PC and mobile both should have a internet connection.
7) You **can backup your chats.** In case your mobile is lost or WhatsApp gets uninstalled anyhow, you can recover your messages.
8) You can **send images, videos, recordings, pdfs, docs etc as well.*