Yeoman actually takes these seed projects and add additional value in providing conditionals (include a certain library, specific modules, etc) and filling out the blanks for variables like project name, module name, etc. They are good for kickstarting a project from the command line, but even better when you have a project already in place where you need to add more files and features over time. Take
Angular 1 for example. I could never remember all the boilerplate that must be written for a service, but with "yo angular:service myService" not only do I get the necessary questionnaire that records the things I have provide, it also includes the right file at the right place with the right amount of boilerplate code necessary. This is just a treat.
At this time, major frameworks like Angular2, Ember and React have their own Yeoman-like tool (ember-cli, ng-cli, create-react-app) that should be used instead of Yeoman. Yeoman is more general purpose and -- most importantly -- extendable to suit your own projects.