I think a serious misconception amongst trainees is that the only thing that matters in grad school is racking up a huge body count of hours at the lab bench. I see them grinding away at the bench hour after hour only to go home too exhausted to do any critical thinking. You have to partition out some of your time to read, write, and more importantly just to think. I've asked these lab bench workaholics how often they are reading and the answers are quite frightening. In my opinion (and for what little it is worth) you need that precious time to just sit and process your own research, your subfield, and what is going on around you in science. This is what sustains the flame of intellectual curiosity and keeps you mentally sharp and focused. At least for me anyways.
Does this sound like utter bullshit?