If my guess it right, it just means that there are other notifications that are less important than the ones that are showing in your status bar.
There are notifications for other apps, but the notifications that are on your status bar now are currently considered more important.
So the dots appear to let you know that there are more notifications that you can't readilly see.
Anyway, if it bothers you, there is a selection available for each app's notifications- Allow notification Dot- that you can turn off.