Depends on ship.
My current ship has a lot of heat reduction so I haven't used a single heat sink in the last 279,000 ly I've done. Granted, a couple of times I was overheating and got heat damage and could've used it, but didn't. It's easier just to repair the ship. I have them just in case jumping out of a black hole gravity well or such. But even there, nothing major.
Now, if I was flying some of my other ships, I might use heat sinks more, but I can't say for sure. Most of the time, I used them during silent running, to be honest.