More seriously, ADHD, among others, is a working memory disorder. A way to cover this is to use "prosthetics" for it, such as a notepad that you always carry with you. If this affects you strongly, train your muscle memory to use it to note down what you were planning to do and to refer to it when you forgot.
In PC-speak, ADHDers have traded RAM for more CPU.
I think writing stuff down, and especially setting notifications is highly beneficial to pretty much anyone. I think it's a great way to offload stuff from your internal brain onto external one. It's kind of relieving when I don't even need to try and remember something. I like to think that it frees up brain capacity for other things.
Like many things, whereas it's just useful for neurotypical people, it's essential for many people with ADHD.