well, i have indoor cats and i dont treat them for fleas. our vet has given up offering us advantage because i keep on telling her that i dont want to put a chemical on my cats as a preventative... if i had a flea problem i would surely use a product. IMO, if you have indoor cats and no fleas you should consider yourself lucky in that you dont have to chemicaly treat your pets... these products are NOT harmless but sometimes, such as in the case of flea infestation, the benefit of using them outweighs the risk involved. i dont even feel comfortable giving my dogs a heartworm med that has "plus" it... that is, the medicine for heartworm plus a preventative med to treat hookworm... why would i dose my pets with a chemical every month for something that they dont even have?!?