I’ve been using futureme for over a decade.

Best use I’ve found is for when I have a huge decision to make. I’ll email myself at some time after the decision must be made; right when I might be having regrets. I explain to my future self how hard it is to decide right now and why the correct choice isn’t clear. Usually with some encouragement of “I hope you know we made the best choice we could”

Of course, I also send some occasionally on birthdays or when I’ve just give through something dramatic — a reminder to future me to remember.