I think a lot of it depends on the real estate agent you find. There could be a lot of negatives with the wrong one.
Make sure you find an agent that invests themselves or has worked heavily with investors in the past. I prefer to stick with ones that invest themselves. Call a few branches near where you want to invest and ask them which agents invest. Then when you get on the phone with that agent, ask them how long they have invested for and how many doors or units they own. One question I love to ask before the agent knows if you are buying or selling is, "Is it currently a buyers or sellers market?" That way you get a truthful answer and that they are not catering or changing it, to match what you want to hear. If they tell you anything besides it being a sellers market right now, they'd be blowing smoke.
The main benefits are that as long as you are purchasing, the seller of the property typically pays the commission of both agents so it is free for the buyer. They have access to the MLS and their social network. This is huge because any real estate agent worth their salt focuses on their social networks and are a wealth of information later about well qualified specialists(i.e. plumbers, electricians) because they have used them before. Also, agents specialize in their area and it would be hard pressed to find someone who knows more about it than them (as long as you vetted your agent well).
Another plus is they usually expedite the process as you aren't looking for the properties yourself or scheduling viewings, they do.
The downside would be that they are paid by commission. Make sure they aren't rushing you into a decision so they get their paycheck faster. Also, if you didn't vet the agent well enough and they are used to their clients paying retail price for a home because they are emotionally attached, they will not be used to you offering a price that is based off your due diligence, facts and metrics that dictate the price you can offer. Often, properties are listed at the emotionally attached price, not what the property is worth as an investment.