When you open blogs creation for your website members then what common problem arrives is that they can create as many blogs they want and by default WordPress doesn’t provides you any feature to limit blogs per user. Well to resolve thus problem network admins use a popular WordPress plugin called Limit Blogs Per User, with this plugin you can easily limit blogs per users in your WordPress Multisite Network.
Simply install and activate Limit Blogs Per User plugin. After activation visit your WordPress Network Admin Dashboard -> Network Settings and limit the number of blogs per users. That’s all, it requires no ther configuration settings. And if you leave it to zero then it will not restrict new blog registration to your network users.