There are many reasons to hire a pet care provider, but obviously the most important one is the welfare and happiness of your pet. When you must be away from home, it is important to try and interrupt your pet's lifestyle as little as possible. As most pet owners consider their pets to be family members, we can assume that pets also feel the same and consider us as their family. So leaving them without proper supervision, care and companionship can create problems both behavioral and psychological for the pet (and sometimes the owner... separation anxiety works both ways).
Most pets like life to be consistent, since domestication pets have indeed become creatures of habit and expect to be fed, watered and to have a certain amount of companionship throughout the day, so by hiring a care provider you minimize the amount of disruption and stress the pet feels when left alone. And of course by hiring a professional care provider you no longer have to feel guilty about asking your neighbors or family members to watch Fido just one more time!
You have the added bonus of knowing that a professional care provider will be consistent and have the knowledge to handle an emergency situation if it should arise. So just as you personally benefit from piece of mind knowing that your pet is in good hands, so to will your pet by receiving personalized one-on-one interaction with someone who really wants to be there for them, providing the companionship and care that they would otherwise miss.
P.S. Don't forget the complimentary extras such as mail retrieval, watering of plants and the home security aspect, adjusting of blinds and lights, etc., creating that lived-in look which helps to deter crime.