Roger Gracie has been the most dominant athlete for years and the only way he seems to lose these days is from strong judo competitors. His two biggest rivals are extremely well-rounded athletes, I mean Jacare Souza and Xande Ribeiro. Both have won their finals against Roger by points by successfully carrying out Judo throws.
Now take a look at Roger Gracie's fight against Leo Leite in the finals of the 2008 mundials. Leonardo was winning on points and at some point you had to get nervous for Roger not pulling guard sooner.
Simply put, having a judo background only adds to you jiu jitsu arsenal. You have more options. You control the fight and I don't know how many times I've seen it before. A great throw can really demoralize your opponent if you lend right on top of them interupting the breathing.
Take a look at the video below as an example of what Judo can do to improve you jiu jitsu game. Cross training in Judo is a great benefit.