My goal is not to disregard, abuse, or cheapen the well-intentioned thoughts behind this phrase. If someone tells you to be yourself, I would recommend taking that as a compliment, thank them, but then move on with life. However, since I hear this phrase everywhere, I'm skeptical. (Maybe too much), but as a young economist, my worldview comes from the perspective of always taking notice of what is unseen. Keeping that in mind, I think there is some unintentional backfire behind this phrase that is worth pointing out.
1 - It suggests that being anyone else is a possibility.
After all, what is the point of the phrase "be you" anyway? Is it a recommendation? Do you recommend that I am myself, or am I intrinsically myself? We both know the answer. I have no say in who I am, but I do have a say in how I act. Our behaviors lie in the future, but our choices exist in the present. So, when faced with a decision to make, the phrase "be you" shifts our attention from the real question of "what do I want associated with me?", to "what does so-and-so do?".
That's not to say you shouldn't look up to people. That's not to say mentors, teachers, or role-models shouldn't have an impact on our decisions. But, if the phrase "be you" is meant to be freeing, helpful, or bring about a natural decision - it may defeat its own purpose.
2 - It can possibly give the misconception that being yourself implies you should do whatever you feel like doing.
Again, it all comes back to our choices. "Be you" can lead to looking to others for answers, but, it can also be taken the other direction. It can also make someone believe that whatever they feel as natural is actually natural. After all, if I have an idea, it's my own. And if it's my own, then it's a part of myself. And if it's a part of myself, then it's who I am. And if it's who I am, then no one can disagree.
3 - It gives the impression that in doing so, everyone will appreciate you more.
Usually, we hear the word "just" behind this phrase - as if our choices are always comfortable and easy when we're "being ourselves".
Nope. Making the right decisions usually means that other people will hate you for it. That's just the harsh reality of the world we live in. I don't think anyone should be controlled by negative opinions. And I know for a fact that if you live without being hated, you're not being loud enough for what you believe in.
To stand for anything is to stand for nothing. But you're unique. You're a monopoly of yourself. If you want to "be you", you're going to have to stand for yourself. Frankly, that means that not everyone is going to like it. But I'm sure many others will really love it.