First, this only really affects administrators with debug developer turned on.
But, as developers, I would think that 90% or more of the time, we are logged in as the admin user and have debug maxed out.
OK, onto the problem: admin_category::add() has a statement where if debugging is turned on, then it attempts to find an admin page with the same name and print out a debug statement. Attaching webgrind screen shots of the performance of this function.
The short story, with this code enabled, its total inclusive cost is 40% of the page load. Without this code enabled, its total inclusive cost is .55% of the page load.
Please perform your own profiling, sometimes things are funny with performance, but some of the raw numbers stand on their own (Like how admin_settingpage->locate is called 46,000+ times).