It's irritating when I am way early on a deadline, and then I get a message close to the deadline (right before or after) reminding me of a deadline I have met with much to spare.

Hello! I sent that to you a month ago / a year ago / etc... and you never acknowledged it. Here it is in my sent messages folder and I'm resending it to you now. You are creating an extra step for me, and also you are not taking advantage of my earliness.