There is always at least one that haven't used chat. Most people are used to communicating in person and then it's rude to not start with "Hello". You directly get a feeling of the stress level of the other, if you should scram or if it's a good time for a question. It doesn't work in remote chat and it needs to be explained for them to understand the problem.

Personally I love the "Hi! Do you have a moment?". "Well, now I have...". Usually the following question will take the rest of my day at least. :-)