Enabled sites crawl on a regular cadence that is provided in the Advanced Site settings. By default, this cadence is every 7 days. This cadence can be updated to be longer than 7 days.
Disabling a site will disable a site from automated crawling. A disabled site can still be crawled manually by clicking the Crawl button in the Sites list.
Disabled sites will not show in the All Sites (Group) but will show in Group reports where the site has been added to the Group.