A search profile determines which pages get crawled and what content gets indexed. In the site-search config file, you'll in the default_profile key that the Spatie\SiteSearch\Profiles\DefaultSearchProfile::class is being use by default.
This default profile will instruct the indexing process:
to crawl each page of your site
to only index any page that had 200 as the status code of its response
to not index a page if the response had a header site-search-do-not-index
By default, the crawling process will respect the robots.txt of your site.
A search profile is also responsible for determining which indexer will be used for a certain page. An indexer is responsible for determining the title, content, description, ... of a page. By default, Spatie\SiteSearch\Indexers\DefaultIndexer will get used. To know more about indexers and how to customize them, head over to the section on indexers.
If you want to customize the crawling and indexing behavior, you could opt to extend Spatie\SiteSearch\Profiles\DefaultSearchProfile or create your own class that implements the Spatie\SiteSearch\Profiles\SearchProfile interface. This is how that interface looks like.