When you assign a letter as “Waived to be seen by applicant”, it implies that you will not be able to see the letter content and that the Letter author was comfortable to mention whatever he or she thinks without being shy or uncomfortable. Waived letters are definitely stronger, more convincing and not biased.
Letters that are assigned “Not waived” are letters that are seen by the applicant and the letter author won’t feel free to write his true opinion about the applicant because the applicant is going to see it. This type of letter is seen as of less strength as a waived letter, but definitely a safer option.
Shall I waive all my letters?
It is definitely a great idea to waive all your letters but there are many unexpected things that would possibly be written in your letters. Remember, you will not be able to see them! Sometimes, letter authors do not remember you well and thus will be writing stuff that might not be in your favor. Imagine if the author mentions that you did well in your Observership, while in fact you did a hand-on clerkship. This will ruin your whole application as observerships are not strong evidence for an author to write something personal about you.
I personally went through this situation but fortunately I didn’t waive all my letters. One of the authors has written Observership instead of clerkship and forgot to mention anything about my bedside behavior. He was in a rush and didn’t write this letter until it was the deadline. I was totally shocked when I saw that he wrote this way especially that I worked really hard with him. I contacted him back and he got the letter changed but imagine if it was waived! I would have never knew the content of the letter and I would be doubting all my life why I didn’t get as much interviews.
Always keep in mind that attending physicians are always busy and they used to be medical students like us, not literature graduates! We hate writing stuff like that, let’s be honest.