There is no one excercise that is "crucial" for development. Excercise in itself, as opposed to being sedentary, is crucial for development.
Can you develop your legs doing squats, deads, hacks etc. without doing leg presses? Of course. However, I've always found leg presses to be an excellent compliment to squatting. I'll often do lps right after I squat. I think it's pretty much a staple for leg training.
Can you live without them? Sure. But IMO you're better off including them.