Often Commercial roofs are patched….Extensively, often to the point of having multi layers, which TPO, PVC, and other membrane based roofing systems are not intended by manufacturer to exceed two layers at localized areas. This gives the membrane a chance to peel up from sun, lack of adhesive (depending on methods used to lay the material) etc. Its very important to keep the roof waterproof and one reason is the insulation that may be directly under the membrane, or lower down between the steel (or wood) trusses. Once that becomes wet, its hard to determine how far the moisture travels and that moisture can compromise other expensive systems through rust, shorting out electrical, and in the wood’s case..rot can form which will structurally degredaate the entire roof……Costly!!