Which of the following is a reason to use existing plug-ins instead of building new ones?

Using existing plug-ins can indeed save time and align closely with requirements, making this the correct choice. When developers utilize established plug-ins, they are leveraging pre-built functionality that has been tested and validated by the community or by the vendors. This can significantly accelerate the development process since they can implement solutions faster without having to design, code, and test the functionality from scratch.

Additionally, existing plug-ins are often designed to integrate seamlessly with the platform's workflow, ensuring that they meet common use cases and requirements that many users or organizations have. This can reduce the need for customization, as the existing solution frequently matches the needs of the project more closely than a newly developed custom solution.

Moreover, while the other choices touch on aspects related to plugin usage, they do not encapsulate the advantages as effectively as the selected answer. For instance, the assertion that existing plug-ins are generally less reliable stands in contrast to their proven nature. The statement about testing can be misleading since while existing plug-ins may require less testing time due to established reliability, they still must undergo compatibility checks in specific circumstances. Performance can vary widely; thus, it's not guaranteed that existing plug-ins will always outperform custom solutions, which can be tailored for specific use cases.