For me the word has no content, it is a way to prime the listener. It's the on ramp to a sentence. "Get ready, I'm about to say something."

Try this experiment. Start your conversations without any pre-amble for a day. Just launch right into the topic. Count how many times you are asked to repeat yourself.

The next day try it by adding "Hey ..." or "So ..." and count again. When I did this there was a 50% decline in need for repeats. Note: Sample size was very small.