What's the other possible product?
Based on its structure, you might consider the order of addition, how much of the benzil vs. dibenzylketone you use, and whether the rate of addition is important.
As you mention distilling the dibenzyl ketone, certainly purifying a starting material can make a big difference...just because it comes out of a bottle doesn't mean it doesn't require purification. Sometimes it's worth it, sometimes it's not...very much empirical or based on experience with similar compounds.
Overall, I think you're right that the lab is designed to give good yield and high purity by the choice of reactants. The question may just be asking, based on your observations and experience, "was there anything you could've done better?". Maybe you ran the procedure perfectly and got an excellent yield of a very pure sample. Probably not true for everyone in your lab.