The short answer: YES!
Fleas and ticks can carry a multitude of disesases, ranging from lyme disease to Rocky Mountain Spotted Fever, and even the plague to name a few. Diseases like these are zoonotic, meaning they can be transferred from animals to humans. Not to mention they're a pain to exterminate from homes once pets bring them inside. Infestations can take months to completely subside, given the life cycle of the flea.
Luckily as owners we can greatly reduce the risk of our pets contracting any of these potentially terminal illnesses, and save the monetary and emotional tolls these parasites can have on our furry friends. Flea and tick prevention is usually applied once per month, and most often covers more than fleas and ticks. Several cover lice, biting flies, and even mosquitos.
The diseases and types of ticks can vary regionally, as does the recommended application season. Always ask your veterinarian about what products are available, and what is most effective.
One word on purchasing products from retailers like Costco, Sam's Club, and Amazon: often these retailers purchase products that are expired, or will expire before they can be used, hence the discounted rate. The manufacturer no longer stands behind these products due to their inability to guarantee proper storage and chain of handling.
Brands like Frontline and Vectra actually guarantee their product when purchased from a licensed veterinarian. The reason is because they can guarantee chain of posession, and the know none of the product was tampered with. No such warranty comes with big box retailers. Often vet's offices will even price match other retailers with smart phone proof.
The biggest word of warning I can give is to ALWAYS buy name brand products with EPA approved pesticides or FDA approved medications. Hartz is a brand that lots of people looking to save a little money will choose. Hartz has caused seizures and death in numerous pets, enough to warrant it's own website cautioning others of the dangers.
If you have questions about what is best for you and your pet, always ask your veterinarian. S/he will be able to give you a specific recommendation and further answer questions regarding specific products (and samples!)