They are really great for planning – my husband and I sit down at least once a week and try to plan a schedule of stuff we need to or want to do. And sometimes it actually happens that way – often not, but at least it’s up on our radar and we are making conscious decisions rather than forgetting stuff completely.
And like the high-five thread, I use one of them to track what I’ve completed during the week, to give myself a lift when I see how much I’ve accomplished!
You can never have too many coloured markers 
– get a dry erase eraser and some of the spray cleaner too.