Optimize TYPO3 site handling for a single site installation
The extension overwrites a method in the core SiteFinder and if your installation has only one configured site, it simply returns that without trying to find the site configuration based on the current page's root line (which is a very expensive operation).
You have only one site (one domain) in your installation and want the best performance? Then you need this extension. It increases overall performance by 13% (or if you need a concrete number: in my test installation around 200ms per request).
Just install it and you're done.
composer require plan2net/single-site
ps: it doesn't harm an installation with more than one site, as then the operation is simply passed on to the default core method