How often should we take them and why?
Some people love them, some people hate them but evidently they're a necessity. The amount of rest you give your body can make a huge impact on progression especially over and extended period of time.
Now everyone will differ here depending on the style of training you do, your level of experience, age, diet on so on so im going to give some key symptoms to look out for to help you determine wether you're in need of a rest day or you're just being slack.
Grip strength: if you're finding it hard to hold onto weights you usually dont this is a key sign your CNS (central nervous system) needs to recover asap! This is mostly due to strenuous training involving a lot of heavy lifting or going to failure and beyond multiple times.
Mind Muscle Connection: if you're finding it difficult to really focus on contracting the muscles properly and find yourself just going through the motions unlike normal chances are you're due for a rest day.
Flu like symptoms: this is the most common one i find that happens personally, i literally train that hard for days on end, my immune system shits itself and as a result I'm left with flu like symptoms (aches, pains, heavy headed) if this happens to you take a day or even two off and let your body reset.
So i could give literally hundreds more examples of things to look for but i find these are the most common ones people seem to ignore or just think "oh it was just a bad session" even though they have gone without a day off for over a week!
I recommend taking a day off at the very least every 6-7 days, I've found personally that a 3 day on 1 day off schedule worked best for me but always do your own trial and error as everyone is different but use that as a reference if you'd like.
I'd be interested to hear from other people in regards to their take on rest days so drop a comment below and if you have any questions related to fitness fire away and il try my best to answer them as best i can.