It is essential to have reservations for certain meals, if you would have a hope of being accommodated, so regular visitors to WDW (and long-time participants in this Disney Restaurants forum) consistently recommend having reservations for such popular meals. However, life sometimes intervenes, and sometimes more than sometimes. While it sure doesn't seem right to occupy three coveted dining reservations slots in one day if you absolutely intend to only use one, back that back a little to you simply being unsure about whether you'll use one, two or all three (i.e., using all three is a possibility), and many folks would not see a problem with it, as long as you conscientiously (attempt to*) cancel reservations you don't plan to use, as soon as you realize you're not going to need them.
* I've noted that Disney generally doesn't traffic in canceling dining reservations. I typically get, "Oh thank you for being so considerate," but it is clear that the reservations agent isn't going to do anything to free-up the reservation slot. They're not really waiting for us to arrive. It'll end-up seeming to the restaurant as a no-show, even though a cancellation was called in, and they'll perhaps account for it by pulling in an additional walk-in. [Incidentally, canceling dining reservations (or at least attempting to) is one of the main reasons why we carry a cellphone at WDW.]