To find out whether the ego is useful or not, we must first ask: useful for what? So let’s see…
Is the ego useful if you want to prevent others from walking all over you?
No, the ego is not your spine, which would draw prudent boundaries. Rather, the ego is what overreacts when you are afraid that you might be perceived as weak.
Maybe the ego is useful when you want to become successful?
Well, for becoming successful the ego is not just useful, but necessary, because having ‘become’ successful implies that you have now identified yourself with your success. Apart from such ego identification, however, why would the ego be useful for success?
Perhaps because the ego sends signals of confidence, which is vital for success?
No, true confidence is rooted in competence, and competence speaks for itself, objectively; it does not need the ego to speak for it.
But what if you are not competent yet? Don’t you need the ego to motivate you to do things, especially things that are hard to do?
Not at all. Your biological drives and adaptive emotions like joy, curiosity, love, and enthusiasm can provide you with more fuel than your will will ever need.
Now what about goal setting? Is the ego not necessary for that?
Only if you also want to be emotionally attached to your goal such that you need the goal rather than just willing it. Needing is an identification with desire, whereas willing is merely a direction of action: if you don’t get what you want, you’re not any less happy, but you are still willing to get after it. All the ego does is make you feel miserable when you don’t achieve your goal, or empty inside when you do achieve it.
But what about the champions in sports, the leaders in business, and the hustlers in finance who often have huge egos fueling their winning spirits?
Well, are they winners because of their ego, despite it, or irrespective of it? If the ego were a proper touchstone of greatness, what about all the ‘losers’ (to use the matching word) with their inflated egos and grandiose visions of how they are ‘above mediocrity’, despite having nothing to show for it? Conversely, some of those commonly called ‘winners’, including many great leaders, are extremely humble. So how can the ego be a general dividing factor between winning and losing?
There is a goal, however, for which the ego can really be useful, which is: wanting to become famous, specifically for having a big ego. Although this would raise a red flag concerning your mental health, it still appears to be a valid sense in which the ego can be good instrumentally. Relatedly, since male fame and boastful confidence are sexually attractive, the ego can also be useful for a man to get laid.
Furthermore, my post Buddhism Debunked discusses a psychological study which found that improved well-being after meditation is positively mediated by the ego. If that is true, we may have a third sense in which the ego acts as an instrumental good, namely, by making you feel better about yourself.
Yet apart from all that, useful or not, the ego simply is what it is: identification with some state (be it physical, mental, emotional, or social); and the more we become aware of it, the less it tends to be.