If ... as a new starter you put an ad in YP or Thompsons, you stand more chance of getting a customer than if you don't. Once you have that one customer who wouldn't have found you any other way, you have a referral source, and as such, it is a building block for your business.
Any method that brings in a customer, is a good business tool... If the cost of bringing in the customer is more than the worth of that one customer, then you do the best job you can and work that customer for referrals and get the value higher.
The advert will have done the job, IE get the customer, it is up to you to get the value out of said customer..