Soy candles typically last longer than a paraffin candle of the same size, you can find each candles specific burn time when viewing the product. Whilst you may pay more for a soy candle initially, you won't be required to make another purchase as quickly as they tend to last longer.
Some of these candles are made with essential oils. Soy candles are great for holding onto and gradually releasing the scent as they burn slower. Meaning you don't get one burst of a strong scent but the slow development of a scented atmosphere.