Selecting a real estate agent is an important part of buying a new home, although not required. A good real estate agent can be extremely helpful and should provide the following services:
Present the homes that suit your needs as you've defined them.
Preview those homes to weed out those that are overpriced, or undesirable in some other way.
Help you determine the difference between a good buy and a property which, because of its characteristics (i.e. neighborhood, market appeal, other faults or flaws) might effect the resale value.
Help you negotiate the best deal for you. And, with a pre-approval your real estate agent will be able to demonstrate that you are a qualified and capable borrower. This will strongly influence the seller, and may make the difference between the seller accepting your offer or someone else's -- even if your offer is lower!