Your teachers used to preach it, give extra points for it, rail about your lack of attention to it. You know that neatness and accuracy matter, but somehow when we're tired and frustrated with the whole business of querying, we tell ourselves that one tiny mistake will go unnoticed.
No it won't. Perfection may be an unachievable goal, but close is where you want to be. I have a relative whose job it once was to sift through incoming mail at a large, prosperous firm. His instructions were to eliminate mail sent by jobhunters who'd commited any sort of mechanical error, an easy winnowing process that saved his superiors' valuable time. Address on the envelope upside down? Toss it. Incorrect spelling? Gone. Begins with "Dear Sir or Madam"? History. And any hand-made corrections, imperfect formatting or obvious cluelessness about the protocols of the business got a letter dropped into notorious File #13.
It may be that your query is never seen by an agent or publisher because some assistant finds a reason to reject it without ever considering the content. It may be that your sample pages turn the reader off immediately because they don't look like sample pages should. That fact can be disheartening, but it can also serve to encourage if taken in the right mindset. IF you study up and learn the correct formatting, IF you correct every single error, IF you research the people you're querying and make sure you submit the way they like, THEN you will begin to learn if it's your writing that is being rejected or just the fact that you can't spell "receive."