Whats the reason why everyone changes the injectors and fuel pump when they do a sprintex install?

The kit itself comes with an extra injector and a T line off of the factor fuel line, is that not enough or something?

Would it be a bad idea for me to just use the T line off of the spintex kit and add the 5th injector without changing the fuel pump or anything?

EDIT: I understanding now, it looks like k-tuner isn't able to use the 5th injector so that is the reason why people are going with bigger injectors and fuel pumps.