There are devices that have many pins for a signal usually for power distribution.
For example, LTM8023 - 2A, 36V DC/DC µModule http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1424,P39569
What is the best practice to draw the schematic symbol and the part definition?
do you prepare a symbol with 24 ground pins etc?
My preference is to make all component pins that have electrical meaning visible on symbol. This gives designer a full picture and provides full control. No implicit pins at all, not even for non-connects