Let's say Binance receives coins connected to these addresses. If they don't comply with OFAC's primary sanctions and OFAC therefore decides to apply secondary sanctions to Binance, US customers will then be prohibited from doing business with Binance. That's a huge incentive for non-US businesses like Binance to comply.
That's exactly how it works, you're right. OFAC's been getting a lot of work done through secondary sanctions. This and the US pullout of Iran and reestablishment of sanctions are a main reason why the EU is thinking to hit back with accusations of unfair/unreasonable action. Shitload of lost money from the two or so years of EU and others (esp Japan) investing in business in Iran all down the drain. Even with the grace period given by the US, it's just so much lost and will be even costlier to resume should sanctions be lifted at some point in near future.
It won't be long before sanctions will lose their worth as an American tool to keep its rivals under their thumb. Their allies are getting real sick with it.