It's more about authenticity and genuine interaction than etiquette. Efficiency drives us to shorter messages. Shorter sentences. Sooner or later, the human part of the conversation is stripped down to its bare minimum and only the useful information stays. It comes eerily close to talking to a computer. Hi. When are you home. At six. Ok. There is no room for the vague thing that comprises a 'real' conversation. That is, if you let this efficiency drive happen. I know I won't. WhatsApp is so popular here that it is assumed that you have it if you have a phone at all. It's so easy to message someone, the bar is so low that it could potentially be the most efficient communication tool. Instead, most of the conversations I have on it are in group chats about the latest news, what's on tv, a funny picture or just joking around. Conversations that are "useless" but fun and genuine. You can use it as a pure and efficient communication platform, but I like it exactly because it's not serious most of the time. Then conversations are much more personal and authentic.
I wonder, if the value of the "useless" conversation comes from the fact that two people have just spent valuable time together for no other reason than to relate with one another. That person is important enough to fritter away time with, and vice-versa. An implied compliment of sorts. My wife and I have recently made some extra attempts in the last two weeks to sit down at home for no other reason than to talk about "useless" stuff sans all distractions and a glass of wine or other drink maybe. I'll report it's been fun and worthwhile. Possibly having the same value to me as scores of efficient texts she could have sent me.