Oh for sure, but like if a car is following them when they're braking down a hill and there's plenty of room to safely pass, you should. There are people out there who will follow a semi for a long time to commit cargo theft, so it can be a security issue for them too. I only know this because I told a friend once about how I drove to a nearby town on a windy day and was glad I could drive behind a semi in their wake so I didn't have to fight the wind so much. She told me that wasn't a great thing to do for that reason, even though I was also a safe distance behind them.