Final answer:
Legacy plug-ins are useful for accessing content on websites or platforms that rely on older standards or specific software incompatible with modern technologies, such as Adobe Flash, but they may pose security risks due to lack of updates.
Step-by-step explanation:
In what circumstance would legacy plug-ins be useful in modern day web browsing? Legacy plug-ins can be useful in situations where newer technologies or updates have not been adopted by specific software or websites. This can occur when a website or digital platform continues to operate using older standards or proprietary software that relies on specific plug-ins to function correctly. For instance, if a site has content developed in Adobe Flash, which is no longer supported by most modern browsers, a legacy plug-in would be required to access that content. Legacy plug-ins can also help in accessing archival content that hasn't been updated to modern standards, ensuring the usability of valuable digital resources. However, it is important to note that using legacy plug-ins can introduce security risks as they may not receive updates and patches to fix vulnerabilities.