Response: Good question Bill, thank you. Ego plays a very important part because it keeps distracting us from our practice. When we sit in meditation or do prostrations, our "ego" keeps interrupting us with "I want to be comfortable! This hurts." When we practice giving, our "ego" prompts "Don't give that away, you might want it someday."
Or how about that "Hey, we've worked hard today, have another slice of pizza." (Okay, I'll personally confess to that one. But I have been working very hard. Honest.) When we want to practice patience, ego pops up with "I don't want to wait quietly in line, I want service now! Where's my double Java Chip Frappuccino Light?" (Had to go to Starbuck's website for that one.)
Ego constantly tries to distract us from our mindfulness to relinquish attachments and aversions because it wants to be the center of attention.
As for a "good ego"—what's good is our true nature. It doesn't ask what's in it for me, but rather, how can I help others.