What do you like best?
It literally couldn't be any easier to get a quick web server stack up and running than with MAMP. Select your home folder, click "start" and that's it.
It comes pre-installed with MySQL, as well as PhpMyAdmin with full root access so there's even an graphical interface for database administration. Perfect for everyone that dislikes using the console/terminal, since you won't need to touch it at all. Everything can be done with a GUI.
What do you dislike?
Configuration is often a hassle, with the config files hidden in multiple sub-folders. Often it's not exactly clear which config files are being used, a simple display in the panel would improve usability drastically.
The support for different profiles/presets is rudimentary at best, nonexistent at worst, so switching between projects takes a good few clicks longer than it'd need to.
Recommendations to others considering the product
MAMP is a handy tool to have installed on your development machine, even in its free version. Give it a try!
What business problems are you solving with the product? What benefits have you realized?
When developing for small clients or working on basic web projects, it's often not worth it setting up a whole staging infrastructure. In this case, MAMP cuts down the setup time for getting to work on a small project.
Of course it's not a fully-fledged development environment like a gulp setup, but it's especially perfect for quick tests and adjustments to classic PHP-MySQL-Webapps. It works fine with Wordpress, Joomla, and nearly all other standard PHP apps.