The AllSpark Key possessed by Sari Sumdac holds a great power, when it was originally just a security keycard. Given a sliver of the power of the AllSpark, the Key can be used to heal damaged Transformers, give life to machines, and control the machines. Such an object holds great power, and with great power comes great responsibility.
Sari had a little trouble getting a handle on that last part.
Oh, who are we kidding? She initially had no sense of responsibility when it came to the Key.
Fortunately, the Key itself has a better idea of when it should be used. Sometimes it can even overpower its owner to accomplish its own goals, even if they are contrary to Sari's wishes.