It’s usually accurate, depending on whether you own a small business or are divorced, in which case it may not be accurate — unless the NPC asks about these circumstances. Note that every NPC is different so you have to do them all.
It’s a good idea to print out the NPC for your own records when you fill out the FAFSA and CSS profile — that way, if the aid package is significantly different, you can ask for a meeting to understand why and sometimes they will adjust it (or explain the difference).