Including some pull sets in your swim program is a great way to incorporate very specific strength work in the pool. Pulling can be done with or without paddles. Pulling takes out any propulsion that you might gain from your legs via kicking, which forces you to generate speed and power through arm action and how you coordinate that with your rotation.
Pulling with paddles ads a level of resistance that will help you build very specific strength throughout the swim stroke. Like any workout that ads a form of physical stress, it’s important to make sure you are progressive in your approach and only pulling with paddles if you are technically proficient. Work on your stroke first so that when you incorporate paddles you are getting stronger using the correct muscle patterns.