Ranked in these QuestionsQuestion Ranking
Pro Asynchronous Turbo Mode
This is Zplugin's unfair advantage when compared with all its competition. ATM postpones the loading of a plugin until after the processing of .zshrc is finished and your prompt is shown and ready for input, offering time savings well north of 80% compared to others' startup times. Essentially this means that you can now be typing that first command you want to execute DURING the extra 1-1.5 seconds that's needed to implement all the plugins in your setup instead of having to wait for it to be done before you can start typing.
Pro Reports costs of each configured plugin
To make good decisions on which plugins are worth the time cost of use, you need good information. Zplugin gives you exactly that with the "zplugin time" command which outputs the exact number of milliseconds required to load each one on the current shell invocation. With that it's easy to know where to reclaim lost speed and invest time in more carefully selecting the features you implement from the troublemakers.
Pro Completion management
With the Z Shell now (as of February 2019) closing in on its 30th birthday, there are multitudes of command completion modules to select from and customize. Zplugin provides a discrete and effective way to use as many as you see fit, as well as taking from each only the types of completions you actually need. This solves a major issue with custom shells, especially for sysadmins which may dabble in many different roles with their machine such as ssh remoting, development projects, container management, etc. Find the modules that give you shortcuts for all but only what you need from each.
Pro Supports Oh-My-Zsh & ZPrezto plugins
Oh-My-Zsh and ZPrezto represent two of the oldest and largest customization managers for Z Shell, each with standout modules that have earned them devoted followings. Zplugin lets you easily access any plugins from either with simple aliases that fetch and integrate them seamlessly within its matrix.
Pro Install individual plugins from their Github repositories
Any experienced Z Shell ninja has a few plugins they've found which exist outside the usual management frameworks within their own individual repos. Zplugin provides a syntax that saves the work of cloning it manually and then sourcing the necessary commands into .zshrc. Just point it at the Git URL and let it work its magic.
Pro Clean startup time of less than 50 milliseconds
Some Z shell configuration frameworks use bytecode compiling to optimize the load times of the plugins you use, but Zplugin ITSELF is bytecode compiled on install. This provides the muscle to enable all the available commands and command variants for managing it without sacrificing any speed.
Pro Bytecode compiling for all plugins
Zplugin pre-compiles each plugin into bytecode, eliminating the need for the shell to parse and interpret them as written on each shell invocation as has been typically done.
Pro Open Source
Con Lack of configuration examples for new users
While the documentation is both broad and deep, it assumes a disturbingly high level of familiarity with both the shell and the concepts behind synthesizing many separate plugins into a complete custom shell. I have strong doubts that any new convert to Z Shell could make good and quick use of it without first getting their feet wet with one of the older frameworks that offer the benefit of many pages of discussion between veterans on how exactly to make it do what you want.