In the example you gave,

// Instead of using this way
myAwesomeArray.some(test => {
  if (test === "d") {
    return test
  }
})
// We'll use the shorter one
myAwesomeArray.some(test => test === "d")

the two functions are not equivalent. In the first case you return either an element of the array or undefined (as opposed to the real boolean returned by the second case). It will work here (as the returned value is either truthy or falsy), but might give you trouble in other cases. The long version of the second function would be the following:

myAwesomeArray.some(test => { return test === "d"); }