A-He told me to leave the room and so I did.
Is the sentence above ambiguous.
I think it could mean:
1-He told me to leave the room and THEREFORE I did.
2-He told me to leave the room and I did so.
Of-course the result is the same in both cases, but there is a change in meaning.
B-He told me to leave the room and I did so but not because he had told me to."
I don't think sentence A is ambiguous. That is because both explanations apply--not one or the other. Sentence B "cleared things up" by conveying a meaning different from that of sentence A. Perhaps the speaker felt the need to clarify what he said with his original sentence.
FW, I do think that there is a point about the degree of authority, but there isn't enough context in the first sentence to see it one way or the other. The addition of 'therefore' does suggest a bending to the authority, but even without, it isn't clear that the departure was a choice rather than a compulsion.