Lifting straps are helpful when using heavy weight for a large body part.
The weight being used may be too heavy for your smaller, auxiliary muscles and those muscles fail before the large muscle you are working!
For example, you may doing deadlifts for the hamstrings. You can use a heavy weight, but your forearms burn holding it before your hamstrings fatigue. Lifting straps would take the stress off your forearms by holding the weight and enable your hamstrings to finish the set. Another example might be doing dumbbell squats or stationary lunges. Again, you may be able to use heavy dumbbells, or may you just want to go high reps, but after 8 repetitions your forearms burn too much to continue. Lifting straps would allow you to do more reps (or weight) without burning out your arms.
In this video, I'll show you how to put lifting straps on the right way! If you ever need to use them, you'll know how!
Download link: Fit 132: How to Use Lifting Straps