On a roofing system, the soffit has two functions: to change the aesthetic of your roof and to protect the rafters, the roof's support beams, from the elements. The rafters deteriorate over time without a soffit and may permit mold to enter your home. These major issues would be far more expensive to solve than simply adding a soffit. Without the help of a remedial firm, mold is nearly impossible to eradicate after it has entered your property entirely.