Maintenance and repairs can be a huge hassle for landlords. Emergency repairs can be needed at any time of night or into the morning. No one wants tenants calling them at 3 am in the morning with problems.
A good property manager will have relationships with contractor and repairmen in the area. In most cases they'll be able to get you a better price than normal. In some cases they'll have in house maintenance that will be able to save you a bundle because you won't have to pay that 90 dollar fee just to get the plumber to show up.
The property management company will know which repairs to prioritize and get someone there fast. Other times tenants are being needy and they'll be able to deal with them.
The property management company will then follow up on the repairs to make sure they have been completed. They'll generally handle paying the repairman and keeping the accounting. Depending on your agreement the cost of repairs will automatically be deducted out your incoming rent. In some cases if the damages are caused by the tenants, the property management company will charge and collect the money from the tenant.
Having a property management company handle the hassle of repairs can save you a bunch of time and give you back your life. This is true especially if you have multiple properties. It will save you sleepless nights and might save you a few gray hairs.