A realtor is a tremendous tool. Not to mention a free one when you are using them to help you buy a home.
A good one can..
Find properties and get showings
Source off-market deals through other agents or their sphere
Refer you trusted vendors from lenders to contractors and everything in between
Negotiate and advise you on the best deal
Creatively help you navigate challenging situations
Advise you on home values, and rents/str rates
Advise on best areas
They are supposed to be an expert, and many of them are. Even big investors on BP like Brandon Turner, trust and use an agent.
Also, clients going at it alone can tend to sell their homes for less than its worth or not get the most advantageous deal on the buy side. Also, other agents may not take an unrepresented party as seriously as if they had a reputable realtor.
If you're buying a house like I said an agent is free to you. And a no-brainer and may be worth their weight in gold if they are a good agent.
Lastly, ultimately they are there to protect you. A solid realtor knows the transaction through and through and exactly how to protect their clients during the complicated situations and paperwork that come with a real estate transaction.
I encourage you to interview several of the top agents in your area and ask the questions that best fit your investment or selling needs to see if they are knowledgeable and a good fit for you.
Best of luck!