Managed services allow a business to not worry about technology--the Managed Service Provider (MSP) handles all the troubleshooting, architecture and budgeting. Automated software fixes minor problems before they turn into major ones.
Most MSPs charge a hefty fee per device. They tend towards servicing larger companies because there's more money to be had. However, I firmly believe that small and medium businesses can benefit from managed services too. In my career, I've seen lots of small mom-and-pop businesses using antiquated, obsolete technology. Managed services can help ease the transition to newer technology and help older devices to keep going with regular, automated maintenance.