Digital printing is more sustainable overall than traditional offset (ink) printing in numerous ways. Offset presses require printing plates, which wear out and must be replaced over time. Digital printing does not. Offset printing also involves more chemicals due to the substantial cleaning required compared to digital.
Paper waste is also a consideration. Most of our jobs are 8.5x11, which means they can be printed 2-up on 11x17 and cut in half with no paper waste. But offset printing starts with much larger sheets or rolls of paper, which requires more cutting and leftover scraps. Much more paper is also wasted in setup and color matching compared to digital.
The economy of digital printing versus offset also reduces waste, albeit indirectly. Setting up an offset print job is quite expensive, but that becomes an ever smaller fraction of the price total as the quantity goes up. This leads some people to print more than they will ever need without factoring in the money wasted for the amount that will go unused. Digital printing has virtually no setup cost, but prices still go down with higher quantities. So you can order exactly the amount you need without wondering if you should have doubled or tripled the quantity to "save money."