Resistance bands are one of my favorite training accessory tools. Not only can you stretch and train in multiple planes of motion but adding them to barbell and dumbbell exercises challenges the muscle at the end of the motion where the weight feels the lightest.
Because the further the band stretches the greater the resistance which helps improve your lockout strength, especially in the vertical plane. And when added in the horizontal plane it helps improve technique and challenges core strength too.
If you are not adding bands to your training, you are missing out on all the fun.