This pattern is used when you hear or think of something, and it reminds you of another related thing. It's like saying 'Speaking of...' or 'That reminds me of...' in English. You often use it to change the topic to something that has a natural connection to what was just mentioned. For example, if someone says 'summer,' you might say 'Speaking of summer, I want to go to the beach.'

It's a very common conversational phrase. You'll hear it a lot in everyday speech, especially when people are chatting and one thing leads to another. It can also be used to show a slight surprise or to confirm a connection, like 'If you say that, then...'.

The pattern is generally neutral in formality and fits both casual and polite conversation, as long as you use appropriate endings for the rest of the sentence. It's not particularly formal or literary, so you can use it with friends and colleagues alike.