Particularly for those living in Europe, or those that have a lot of international friends - all with phone numbers from different countries - it's a godsend. My phone bill would be ridiculous if I were texting my friends in Sweden or Brazil from my Dutch SIM. iMessage for similar reasons.

Also the group messages are great. My housemates and I all talk via a WhatsApp group. It makes it far easier to hold a coherent group conversation when some of us aren't at home. SMS would be a ballache.

Oh and GIFs, voice messages, and videos can be sent in messages. Free calling too. I can call my friends in Australia for nothing, and it's not a bullshit experience like Skype.

I almost never send true blue SMS any longer.