The disadvantages of using proprietary software include limited customization and potential vendor lock-in, restricting users' ability to modify the software to their specific needs. Proprietary licenses can result in high costs for users and may limit access to necessary updates or technical support. Additionally, users have minimal control over the future development of the software, as decisions rest solely with the vendor. In contrast, open-source alternatives often offer greater flexibility, community support, and lower costs, leading many to prefer them for certain applications.