I think self-esteem is essential for just about everything in life that we try to manage as adults. If I do not invest in myself in a very real way, it makes it very difficult to stand up against wrongs (no matter how minor), and to be there for others. When one is lacking in esteem, there is a tendency to be very self-absorbed and always monitoring one's actions, words, feelings. To be constantly second-guessing oneself, inwardly asking ourselves things like, "Oh, did I do that right?", "Do they like me?", "Am I okay?", "How am I doing?" takes us out of the present moment where life is actually happening.
So, what is a "very real way" to invest in oneself? I like what my friends in AA have to say about it: If you want self-esteem, do esteemable things.
Basically, self-esteem comes with practice, I think, much more than through self-talk. Self-talk and affirmations can help, but we can also very easily follow those along into the usual mental process that has us thinking less of ourselves. If we can just rise to the occasion as things occur, do what needs to be done, accomplish tasks, meet challenges -- without giving in to patting ourselves on the back, either, which is just another way to have a dialogue about how we're doing instead of engaging in life at this moment of now -- but simply to be productive and follow through, then we suddenly realize that we've found ourselves just feeling good about who we are.