As a WordPress user, one has the option of either installing already developed plugins, or developing them from scratch. Both of these options have pros and cons. As a general rule, it is always a good idea to use supported and well-reviewed plugins from the WordPress community when those plugins offer the functionality needed. This is because these plugins are popular and well maintained by the community. They tend to be more robust to software upgrades than custom plugins, and they do not require a constant investment of resources to keep functioning. This approach also tends to be feasible because there are already tens of thousands of such plugins already available.
That being said, there are times when it makes sense to develop a custom plugin. If some special functionality is needed that has not been addressed by the community, then it makes sense to develop a plugin for that purpose, especially if the functionality is very specific to one project, and not of more general interest to the community. In the case, committing the resources to maintain the plugin may be worth it. Another use case would be where an existing plugin has most of the functionality needed, but extending it would provide a more complete solution. This is a more hybrid approach that requires less investment than a completely custom plugin. Of course either method could allow a custom addition of a plugin to the broader community.
