I often use resistance bands to "redirect" tension during barbell lifts, allowing me to focus more on certain muscle groups. The sweeping deadlift is a good example.
Another awesome application comes from the mad scientist, Nick Nilsson. You attach bands outside of a 25-pound plate on each side of a barbell that's been set up for bench pressing. Then you put your forearms inside the loop of the bands.
When you press the barbell, you consciously focus on pushing against the bands, trying to press your elbows in. This will shift the stress away from the shoulders and onto the pecs.
This is actually the correct way to bench press, but very few people do it. Instead they simply press the barbell up, moving the shoulders toward the ceiling. This both shifts the stimulus away from the pecs and increases the risk of shoulder injury.
Note: In the demo I'm not using weight outside of the bands so that you can more easily see the proper set-up. Normally I add weight to properly load the exercise. Total weight should be around 40-60 pounds less than what you use on a normal bench press.
How to Do It
Put a 25-pound plate on each end of a barbell. It should be around the middle point of the sleeve (use a collar inside the plate to secure it).
Wrap a small resistance band outside of that plate on each side.
Add weight outside of the band, so that you have the proper load for your set. Start with around 40-60 pounds less than what you'd use on a normal set.
When you're lying on the bench, pass your forearms through the loops of the bands.
When pressing the weight up, focus on pushing the elbows in and pulling the bands.
I love this exercise because it targets the pecs better than standard benching, it teaches optimal pressing mechanics, and it greatly reduces shoulder stress.