Physical books? Sometimes I like just kicking back and reading one but I'd be lying if I said they were a more efficient reference when compared to digital information. I think the downside to digital references, especially the internet based ones, is that distractions are plenty (like haphazardly getting sucked into that bizarre part of Youtube for an hour before coming to your senses). So I think it depends on how much you like books and if they fit into your life.