I think that adding educated, informed or estimated to 'opinion' is better for emphasis, rather than adding the redundant (not really verbose) personal.
People can use it to imply "But I understand and accept that others may have different opinions." It's particularly apt if you are part of an organization and the organization's "official" stance is different from your own.
I agree with Clive that if you use it too often, it sounds silly, but if you really want to emphasize that your opinion is not shared or may not be shared.
Thank you for the enlightenment. I guess it's not entirely wrong after all. I also think that when we include 'personally', it emphasizes the fact that the opinion is not influenced by others.