This check determines whether the number of web applications in the farm is in accordance with Microsoft recommendations.
SharePoint web applications are logical abstractions on top of IIS websites. One SharePoint web application can consist of multiple IIS sites and content databases (where site collections are stored). Additionally, a number of timer jobs are created for each SharePoint web application. This creates overhead and requires more hardware to run fluidly. Therefore, it is recommended that the number of SharePoint web applications is kept below 20 for each SharePoint farm.
Creating new web applications is recommended in the following scenarios:
- Web applications with different authentication methods (different IIS application pools)
- Dedicated web application for My Sites site collection
Creating multiple SharePoint web applications is unavoidable, but because they create a lot of overhead it is recommended to keep the number to a minimum. When applicable create an additional host-named site collection instead of web applications.
Additional information can be found in the following article: Web application limits