Many companies offer ongoing pest control services, for homes with persistent pest issues. While homes in rural and woodland areas are liable to more pests, you will often get repeat outbreaks of things like bedbugs or urban mammals, like rats and mice, in city areas. Your pest control service should be able to advise on whether or not persistent treatment is necessary, and will give you tips on how to make your environment less hospitable to pests in the future. Pest control actually starts outside the home, then moves in - think of this as the company first dealing with the root issue, then resolving the symptoms of the issue.
Some pest control companies will insist on monthly visits to manage the perimeter of your home, in order to manage the actual cause of the infestation. This is good for prevention. Others will visit quarterly or less frequently, and do a more thorough service, which could include a perimeter fix, and a treatment to both the outside and inside of your home (it all depends on what pest issue you have).
Our advice in terms of whether to choose an ongoing or one-off treatment really comes down to risk. A rodent infestation, for example, may be fixed with a single visit, and a repair or modification to your actual home (something as simple as fixing an entry point in your exterior wall). However, if the environment around your home is fertile for rodents, it's better to continually manage your perimeter to avoid them coming into your home in the future and to rid your house of them when they do sneak in.