The reason you would want to prune Rugosa bushes is to make them more attractive in your garden. They will propably bloom better also.
Wild Roses such as Rugosas can be left for three to five years with almost no pruning other than removing spent blooms.
However, all dead or damaged branches should be removed each year, or whenever you find damaged or dead canes, usualy late winter or early spring.
Rugosas grow only really well in the colder regions, and shouldn't be planted in California, Florida and the South.
Occasionally, an old cane can be removed at the base to promote new flowering canes, or to prevent the rose bush
to become over crowded or invasive.
These pruning techniques for Rugosa roses of minimal pruning usually result in larger and more attractive rose plants.
But if you would like to keep the rose plant smaller, you can prune them every year as though they were large brushes.
However, I recommend the minimal pruning as the best pruning for Rugosa roses.