Is it bad to include a lot of files in PHP like it is for file based Sessions?

Question

After reading about how file based PHP sessions are not the greatest for performance, it has me thinking. Does this mean a PHP script including a lot of files is bad as wel

Answer 1

Another option is to "lazy" include files, eg, require_once them before using them (example instantiating a class) so that a whole load of unused includes won't (kind of) happen.

I've used a Zend feature about this (register autoload) but I do not know if it is generic to php or if it is not but exists to other frameworks...