Ego is mostly an obstacle in scholarly writing. You should have a healthy sense of being competent and having a perspective worth hearing. (False humility is pretty much worthless.) But ego interference can be crippling, leading to

1) Writer's block. What you write is never good enough for your own over-exalted sense of how good a writer you are. Therefore, you write nothing.

2) Inabilty to take criticism from others.

3) Inability to be a good critic of yourself, to evaluate what you've done the day before with a cold eye.

4) Lack of generosity toward previous scholars and critics.

etc...

Egotism manifests itself both in being overcritical of one's own work and in not being critical enough. It's a matter of calibration. Use ego when it helps you, discard it when it doesn't. (Easier said than done!)

Imagine me playing the clarinet. I was today just exploring the tone quality of each note on the instrument. Some were more in tune than others; some had a more pleasant tone quality. That's information that I can use. If I make it about the note: "that note is not in tune," that is more useful than a statement about myself like "I am a lousy clarinetist." If a note sounds good, I am thinking, that sounds good.

I use the same principles for something I am very good at (scholary writing) and something I am definitely not good at (clarinet playing). The wrong calibration of the ego would be harmful to either one.