From my experience, it is important to close the period for sure to prevent anything from posting to that period and having numbers change. The thing that sticks out the most to me with the importance of this involves taxes. If say you pay in monthly or quarterly income taxes, or sales taxes monthly based off of figures you pulled from a certain period, if anything ends up getting posted later to that period after you filed your taxes, it could change the amount that should have been reported, if you don't file a tax amendment. This could cause issues down the road such as if you were audited. I worked for a company once that never closed their periods, and we had a lot of questions from our accountant that was hired at year end when he was dealing with our taxes, seeing that figures reported from some periods didn't at the time match the books.