With unmanaged hosting you are responsible for handling the server admin duties. But with managed hosting, that responsibility belongs to the web hosting company. Unless you are a someone that knows your way around a server (with knowledge of patches, updates, viruses, etc) you will most likely want your hosting service to be managed.
Of course unmanaged hosting is cheap is comparison to managed, but it’s absolutely worth the small amount of extra money. You’ll sleep better knowing that someone else is fully managing your business hosting.