The main advantage of using a virtual machine (VM) in computing is the ability to run multiple operating systems simultaneously on a single physical machine. This enables efficient resource utilization, allowing users to test applications in different environments without hardware changes. VMs enhance security by isolating processes and applications, reducing the risk of system conflicts or malware spreading. Additionally, they simplify server management and disaster recovery processes, as virtual machines can be easily backed up, cloned, and migrated to different hosts.