If you don't compete in Power or Olympic lifting, then absolutely use straps.
I use them for all sorts of pulling exercises, even higher rep pulldowns, not just my heaviest sets. By not having to worry about your grip giving out, you can focus more on the back muscles doing the work. This is one of the most common missing links in most people's back training (especially the lats)
In fact, I hardly grip the bar at all and act as if my hands are just extensions of my arms. This creates a more focused pulling angle and allows you to pull with your back.
Anytime you squeeze a bar tightly, the lower arms (and upper arms to an extent) will contribute significantly to the overall pull effort.
If you're worried about grip...work it separately.
BTW....SDL's are one of those exercises where bar position is of great importance. If your grip gives out or weakens during the movement, the bar can roll in your hands which can increase lumbar stress. Using straps will allow you to focus on hip movement, bar position, and pulling with your hamstrings.