I would assume that it is a bit like training you muscles or any other form of sports. It’s a common practice to take breaks, as the body requires the time for improving condition and muscle build-up. Depending one the kind of training and the intensity one day of training can be followed with up to three days of break. This doesn’t mean you do nothing these three days, but either something completely different (switching between muscle and conditions training for example) or with a much lower intensity. The sport itself only serves as a stimulus the body should react to, and the latter requires a lot of energy and time, thus the breaks.
There are indeed some studies to be found on the matter of taking breaks in learning. However, those are usually investigating taking short breaks during the courses. An interesting example was a Spanish study where they introduced a 10 min break to test its effect on reading comprehension. The interesting aspect is that the students taking the break performed better even though the 10 min break wasn’t added, but instead 10 minutes of learning was exchanged with the break. So they spend time with a break while the comparision group was still learning, and still they performed better. Other studies imply a similar effect for longer breaks (a few days or even some weeks). Unfortunately the tested groups are usually rather small (50-150 participants) and localy restricted (one course doing one specific subject). So this needs to be taken with a grain of salt.
I think that the benefit of breaking apart long learning sessions into smaller pieces distributed over the day is better researched and somewhat proven, though.