Why is search disabled by default for anonymous users? I noticed that search is only permitted to logged in users on drupal.org and I'm wondering why. Apparently it's also disabled for anonymous by default in Drupal 7, and I see people discussing how to enable it to anonymous users, but no-one explains why this default setting exists.

I assume there's a performance issue or opening for a DOS attack?

I'm particularly interested at the moment because we're currently having DB issues (overloading the max permitted connections) and we have D7 with search enabled for anonymous users.
In Drupal almost all permissions other than access comments, view published content and exceptionally use text format filtered_html are disabled by default for anonymous users. There is no specific reason for search other than the rest. 

It is up to you and the purpose of the site you want to build, which permissions you want to give the users.