What is a Spartan diet?

Could you elaborate on the concept of a Spartan diet? I'm curious to know if it's a restrictive eating plan similar to other diets, or if it has unique characteristics that set it apart. Also, I'm interested in learning about its potential health benefits and drawbacks, as well as any scientific evidence that supports its claims. Lastly, I'd like to know if it's a suitable diet for everyone, or if there are certain groups of people who should avoid it.