Depending on your instructor it should not be an issue if you just want somebody to have a quick look over your flight plans. However if you are flying long distances the chance of things changing en-route increase. Being a pilot does mean you need skills that need to be employed competently and independently, on your own. This is why you have to do a whole separate part that involves learning to navigate, not just to find your position, but to successfully avoid dangers such as RAs, CTA and terrain you should avoid overflying. The instructor should not put you up for a test if you are not well on your way to conducting a cross country navex independently,including the planning.