Since the number one cause of drain blockages is hair, the bathtub drain strainer will prevent hair from seeping into the drain. It will also prevent larger items like a wedding ring from slipping down the pipes.
In-drain hair catchers are the best because they grab hair as soon as it enters the drain. The only point to take note of is that the in-drain catcher sits inside the drain and so you'll need to check on it from time to time to ensure it is thoroughly cleaned.