Cockroach Damage
Cockroaches cause damage in 4 ways:

1.  Too ugly to live.  They are butt-ugly so nobody wants to look at them.  People just don't like them running around on their countertops, food, babies, etc.  They don't like cockroaches falling from the ceiling and landing in their mouths while they are trying to sleep.  The sight of cockroaches can cause considerable psychological or emotional distress in some individuals.

2.  Disease Transmission:  Cockroaches mechanically transmit numerous diseases.  Cockroaches produce odorous secretions that can affect the flavor of various foods and have also been implicated in the transmission of diseases. Disease-producing organisms such as bacteria, protozoa, and viruses have been found in cockroach bodies. Different forms of gastroenteritis (food poisoning, dysentery, diarrhea, etc.) appear to be the principal diseases transmitted by these cockroaches. These disease-causing organisms are carried on the legs and bodies of cockroaches, and are deposited on food and utensils as cockroaches forage. In addition, there is ample evidence implicating cockroaches in the transmission of hospital acquired diseases.

3. Allergies  A host of studies recognize cockroaches and their byproducts as strong indoor allergenic agents.     Sensitivity to cockroaches is linked to infestation levels; the more cockroaches there are, the greater the chance of hypersensitivity.  Since the prevalence of asthma in children been increasing steadily over the years, the need to control cockroaches is more important than ever. Children in the inner city have higher levels of exposure to cockroach allergens than most children, and this increased exposure to cockroach allergens is one key factor responsible for the higher prevalence of asthma in poor urban areas.

Not surprisingly, a significant reduction in exposure to cockroach allergens can be achieved through extermination of resident cockroach populations. In a recent study,  repeated measure of cockroach allergen levels in floor dust samples taken from an urban dormitory were similar despite weekly vacuum cleaning. However, when regular vacuuming was combined with cockroach extermination, the level of cockroach allergens fell 5.5 times. Currently available pesticides have been shown to reduce cockroach populations by 85 to 100% and maintain reductions for at least 3 months.

4.  Feeding Damage:  Most roaches infesting homes like starch and will chew on starchy items.  The German cockroach will feed on books and their bindings thereby destroying them. It is also fond of starchy food like cereal, sugary substances and meat products.  The larger roaches will also chew on paper products damaging/destroying them in the process.  In addition, the fecal material from feeding can contaminate food and stain other products.