You should instantiate an object only when using, for example: A Car class where you need to store the card and use some method of it.
Class loading
But in your example you gave the idea of importing a class to your PHP file and really this is a problem since you will be loading items that at that time will not use, besides having to fill your include code.
For this second case, PHP has the spl_autoload_register, an Autoloading that already do all this service for you. I’ll leave the Autoloading documentation link below so you can get more in-depth about.
http://php.net/manual/en/language.oop5.autoload.php
Only create an object when using.
– rray