DO IT FOR MIND-BODY CONNECTION, PROPRIOCEPTION, AND BALANCE.
People often make an exercise harder by increasing time under tension or the range of motion, but very few add another equally important element: decreased vision.
Have you ever gotten up in the middle of the night to go to the bathroom and felt a heightened sense of awareness? This is because your eyes (more specifically your pupils) expand in low light in an attempt to capture all of the available light. Training in bright light (which almost 100% of the time we do) makes our eyes lazy just like training in sneakers will make for lazy feet. On the other hand, training in low light forces you to concentrate on the task at hand and really hone in on the mind-body connection. Lastly, your bodies awareness of where it is in space (proprioception) is heightened when you are in darker spaces and when you are barefoot.
Try doing a whole training session barefoot with the lights off at least once per week. Use that time for exercises that challenge balance and stability. Personally, I enjoy some single leg deadlifts (pictured below) and lateral lunges. You can also do more than just your lifting sessions in the dark. Try sport specific drills that challenge reaction time and agility like hurdles, jump rope, speed bag work, hitting a baseball, or saving pucks.