An interest basic thread, sometimes we use phrases for the sake of it or because we like it, it enriches the language too. I'll do two,
by the way: a common phrase used to introduce a topic or someone during the middle of a discussion. If I'm talking about something to Mr.X and suddenly you drop in, I would stop as say to Mr.X: By the way, meet my friend, Mr.SuN.
by and large: another phrase that means on the whole except a few, like taking the majority view. If there is protest against a hike in petrol prices with only a couple of clashed or arrests, we would say: The protest against the recent hike in petrol prices in the city was, by and large peaceful.