Your occult book was probably referring to the finer "rules" of traditional candle magick.
When performing candle magick, it is generally suggested that only "virgin" candles are used, candles that have never been lit or used before, as it provides a clean slate for the working and ensures that residual energies from previous workings wont interfere with the task at hand.
It is also done for practicality, as when doing traditional candle magick each candle is blessed, consecrated, and charged for the specific working, before the actual working takes place. This is referred to as "Dressing a candle" and it isdone to remove the preexisting energies and replace them with new energies aimed toward the purpose of your spell/working. The two main ways to dress a candle are to either attract, or repel, certain energies using water or oils. If you want to attract something to yourself, rub oil from the top to the middle, and then from the bottom to the middle of the candle. If you want to repel, rub oil from the middle to the top, and then from the middle to the bottom. While doing this, focus on the desired outcome of the working, energizing the wax with your energy & intent.
If the candle is allowed to burn completely, it is suggested that the leftover wax is buried on your property (if for attracting) and away from your property or at a crossroads (if for repelling). Since it is your working, do what feels right to you. This is said to complete the ritual, and hence, why each candle can only be used once.
For your purposes, its fine to reuse candles. If you ever get into Candle Magick as a primary practice, then you might find it more appealing to only use virgin candles. It comes down to personal preference.
O, Sinix. "The Complete Candle Magick Guide."The Sinix Sanctuary . Facebook, 24 July 2013. Web.