I haven't read all of the information Manning is alleged to have leaked, so I don't feel I can remark in anything like complete certainty on whether any of the information he disclosed may have put others in jeopardy or risked compromising long-term operations.
What I will say, from what I have seen, is that it seems apparent his actions were ones he felt he had to make as a matter of conscience; that at least some of the information brought to light regards truly despicable actions for which others ought to be held accountable, and that the espionage charges brought against him seem disturbingly inapt. While not strictly defined as such, the term "espionage" seems to imply passing of information to interested parties either for material gain or to the benefit of an enemy or foreign power; it's clear Manning's intent was neither.
I also find the "such conduct being prejudicial to good order and discipline in the armed forces and being of a nature to bring discredit upon the armed forces" part of many of his charges disturbing, as it amounts to admitting that true accounts of the deeds of members of the armed forces are harmful to morale and discrediting to the service. That seems like good cause to shape up, not cover up.
I fear that the government's case against Manning- and for that matter, Snowden- is as much about sending a message to potential whistle-blowers as it is about their actual activities. By and large, I get the impression that the leaks are less about enemies of the state getting hold of the information as citizens of the state doing so. There are always going to be secrets, but I'd like to live in a country that wasn't so damned afraid of its own people knowing the truth.