Development plugins are plugin implementations that explicitly set the developmentPlugin property during initialization. Plugins marked as developmental are not loaded when the load-development-plugins setting is not set to true in the configuration file.
Development plugins are not loaded by default. This is due to the reason that in most setups, these plugins won't be used, necessary, or even useful. If unsure, leave this setting untouched (i.e. empty or false). If you are missing a functionality, consider writing a plugin for the system.