I'll be really honest. I haven't done it ever and I regret it. I AM planning what I call a monk year now. I also interview people that have done it so I've been on the other side.
Conclusion: It's really all about a plan first, discipline about the plan's boundaries and self-confidence when you present your achievements after. Else you may be viewed as a lazy hedonist.
E.g., My PLAN is to take year to train for an Ironman. That's about 4h a day on average. I'd also eat well, stretch and keep up with the ancillaries of such hard training to prevent injuries. Then I'd be studying 4 online courses à day in whatever I want. My goal would be to finish a few nanodegrees and a few specializations on Coursera. Courses would be about 5h per day. Every day, non-stop. At the end, I would have done one Ironman AND add a whole lot of skill to my arsenal. It's not cheap - calculated it to be about $40K so far with a mortgage and rent to pay but I'm working on creative ways to lessen this. Last but not least, I have three non-profit projects I want to do. One huge dream, one medium, one small. If I went to an interview à year after this starts having been disciplined enough to accomplish even 75% the above, I'm pretty sure not even the hardest interviewer would be skeptical.
Basically, I view the monk year as the year where I still grind. But I grind to add value to yours truly NOT the corporation.