@TeddyBoomBoom and
@Decremaster
There isn't really anything to disagree on.
Getting a DO letter is beneficial to apply to DO schools in most, if not all cases (especially if the school requires it). Are there those who get in without DO LOR, of course. But they have a little more jobs on their hands to talk about DO field and they sure aren't qualified to apply to schools that require DO LOR.
Schools aren't going to assume you know ins and outs of DO just because your parent is a DO. They need proof and your job is to provide that proof by getting a DO letter.
Interview is the 3rd step in the process (usually). The letter comes in before the interview (in most cases). In order for someone to get an interview and talk about their experiences and knowledge of the DO field, he/she needs to get the interview in the first place. In order to get an interview, you need to provide as much information as you can in the first 2 steps of the application process, which includes a DO LOR.
Who cares if your parent is a DO if your can't get an interview to talk about it?
Do the most you can to get an interview to talk about yourself, which includes getting an DO LOR to show your initiative in DO field.
DON'T let schools just assume you know. Show you know.