This check determines whether the total number of Search Service Applications is exceeding the supported limit.
Search Service Application provides the enterprise search functionality to one or more SharePoint farms. It provides mechanisms to index SharePoint and non-SharePoint content sources, query the indexed data and provide search results, where required. The search architecture contains search components and databases. How you structure the search architecture depends on where you intend to use the search: for the enterprise or for internet sites. When building the search architecture, you should take into account considerations such as high availability and fault tolerance, the volume of your content and the estimated amount of page views and queries per second.
Multiple SharePoint Search Service Applications can be deployed on the same farm, because you can assign search components and databases to separate servers. The recommended limit of 20 is less than the maximum limit for all service applications in a farm.
You have to make sure that the number of Search Service Applications is within the supported boundaries. To check your service applications, go to the Central Administration > Application Management > Manage service applications.
Additional information can be found in the following article: