Comment by matsemann
The opposite is true as well. If someone pings me hello, I might not answer immediately because I don't know if what follows will be a big or small thing, but after having replied I feel obligated to continue answering. So my decision is to not answer until I'm less busy.
If they however ask a question no hello style, I can quickly gauge if I can answer it immediately, or I should wait until a better time for me.
So the no hello might get an immediate response, the hello will wait until I can handle whatever.
And if they ask the question and I determine I don't have the bandwidth to switch or immediately answer I can kindly reply such information. They're more likely to get a reply faster by skipping the hanging and dangling hello. "If it's important, they'll leave a message."