Reminders offered only on future events
I use Calendar both to record planned meetings as well as to record my historic activities during the day to be able to invoice clients later. It is rather annoying to get a reminder on historic events immediately after recording such events, but it is quite helpful to have automatic reminders on future events. You should add an option to only offer reminders on new calendar items if start time is later than current time. If start time is in the past do not offer an automatic reminder.
Randy Geyer commented
Not only is it annoying to immediately remind you of a past event, It's idiotic. Let's introduce the developers to the if statement!