Yes, I would definitely want to leave notes trying to explain why I did it and trying to absolve anyone from guilt or the worry that they could have even been able to stop me.
I've had the odd horrible person in my life but mostly good people who it might come as a shock to. Not that words are really going to make them understand but it's something I guess. I've been grateful when loved ones who have passed left me letters (from natural causes).
The person who I would say is a major part of initiating this path wouldn't feel blame or guilt anyway because (in my opinion), they are a narcissist and see themselves as a victim.
I do get where you are coming from though. I think when I initially wanted to ctb (age 10), I even drafted a note blaming them! Guess it depends on whether you have any nice/supportive people in your life. Also think that it can be damaging to you to act in a spiteful way- even though they likely deserve it and even though it's not really spiteful to not do something. Just think- if you have the strength to be the better person, although you might resent it, it might feel better to have done it- so your mind is more at peace if you go ahead with it. Whatever you decide, I wish you peace.