WhatsApp integrated Signal's end-to-end encryption¹ into their communications platform.

Nearly everyone I know uses WhatsApp. This change made the platform much more secure for everyone. It's on by default and works transparently. Since then, at least one government was unable to compel WhatsApp to produce messages² from users under investigation.

I also have Signal installed but nobody I know uses it so its utility is diminished. I told some friends about Signal; they installed the app but won't use it because they can't message anyone except me. The only times people talked to me via Signal was during the temporary WhatsApp blocks ordered by my country's government.

¹ https://whispersystems.org/blog/whatsapp-complete/ ² http://www.forbes.com/sites/parmyolson/2016/05/03/whatsapp-f...