The setting Show number of jobs in category on the Configuration Options page with possible values YES or NO allows you to either make the number of jobs show up or not.
They are configured to show up by default, but in some cases you may consider hiding them like when enabling the job feeds integration with Indeed.com or other providers - when you do that, in every category there will be thousands of jobs, but their exact number won't be available. The reason for that is in order to do, it will be necessary to make a separate query for every category and feed provider, which will make the loading of the home page very slow, so it's skipped. So you may hide the number and just allow the users to click on the category and then check the jobs or use the job filters available on the results page to further filter the jobs and find the ones mathing theyr search criteria.