We use this expression to give the main reason for something, either positive or negative, when there are several reasons for it.
You can use this phrase in ………… language.
A: Why didn’t you come out with us last week? We had a really good time.
B: Well, I had a different appointment for a start. And I don’t like the club you went to.
A: Why don’t you like that hotel?
B: The rooms are cold, for starters. And the location is not that good.