Scaling down the size of pins can be useful because for some people they look too big and out of place on the map. Scaling down the size will greatly improve the look of the map and could reproduce better prints. Specially when you have a lot of pins on the map. Give it a try and see the difference.

How to do it? When creating a new map select the size from the dropdown box, or if you already have a map click the "Edit Map" button (the one with the yellow pencil) from the map toolbar and select the pin size from the "Scale Down Pins to" dropdown box.