So plotting something by a date series works great. However you can not plot more than one thing against a date series at the same time. you always have to select a set of data for the y-axis. this is a real weakness in your chart offering, it makes for cluttered hard to read dashboards.
For example if i have 3 sets of data that happen weekly and they are related in some way. I have to make 3 separate charts. If you have a lot of data that means that on a dashboard you can often only see 2/3 charts at any one time.
Freeing up the y-axis so that it just shows numbers would solve this. It's pretty common in most chart offerings.