For most back exercises, I use a hook (or thumbless) grip. I do find that this helps me to focus on pulling with my late as opposed to my biceps. Additionally, I focus on pulling from the elbows, not the hands/wrists, which also minimizes biceps involvement and places more emphasis on the lats, and allows for a ROM more complete and focused on the lats than being dominated by the biceps. Another useful trick is to think about pulling the bar apart as you pull, which further helps focus on the lats as opposed to the biceps. With these things in mind, I do not feel straps are necessary, although they can help to the same ends as the hook grip while ensuing grip strength (which is reduced with a hook grip IMO) doesn't end the set before muscle fatigue does. For most exercises, I do not find straps to be necessary though, even weighted Pullups, and I do believe that working and improving grip strength is a good idea and useful both for overall strength and performance as well as forearm development.