If its important write it down

For most students there is a real benefit in writing stuff down. This is why writing study notes is such an important part of exam preparation.
Theres something about the process of writing something down going through the motions of putting pen to paper that helps information stick in our memories. Your teen is unlikely to remember something simply by reading about it once. A good rule of thumb is that if its important enough to know for the exam, write it down.
I would also say, that in this digital age where 3 year olds know how to use an iPad better than I do seriously , your teen might never hand write anything anymore and thats a discussion for another day , and if thats their preference and it works for them, then typing the important stuff can be just as good as hand writing.