What really defines a great dinner roll is its softness and springiness. For perfectly fluffy rolls, try adding mashed potatoes to the dough.
The soft mash allows the dough to hold onto more moisture, and also helps to keep the rolls fresh and soft for longer, instead of quickly drying out after you bake and store them.
Potatoes work like pre-cooked flour and water, resulting in improved moisture retention in your rolls. Potato starches also allow for fluffy rolls that won't stale quickly.
The mashed potatoes need to be smoothly mashed and fully cooled, as hot potatoes change the texture of your dough and could even kill the yeast.
You'll also want to follow a recipe for potato rolls, rather than trying to add mashed potatoes to an all-flour roll recipe.
Mash changes the starch and moisture content of the dough, so other ingredient ratios must be adjusted accordingly. This isn't a recipe you'll want to freestyle.