People like to acknowledge your question while they think of an answer. Similar to er / um / well / I'm glad you asked that question etc etc
It drives me mad too ... I think it's an attempt for dominance - it sort of implies that they've been interrupted and are taking back control of the conversation.
It's enooooooooooormously irritating
Know what you mean Hazel, I can't stand.......chillax or when someone tells you something and then says.........yeah at the end grrrrr.
Or the expression.............back in the day..........which seems quite common lately.
Don't like it when people talk using their hands to do inverted commas either.
Or when people finish the end of your sentance for you.
Throwing the word "obviously " into a sentence such as " obviously we used to...... "
Well, as you've only just told us, in what way was it obvious before?
Don't even start me on the word " amaaaaaaaaaaaaaaaaaazing" which seems to apply to everything these days.