This one is useful if you use a mac and an iphone.
i like my reminders on my phone, I like having them synced to my mac.
i dont like getting beeped at ten times when I have something to be reminded about. once is enough.
to turn off the reminders on your mac (so that only your phone beeps)
open ical > preferences > advanced
tick ‘turn off alerts’
now you will not get reminders on your mac!