I think it's just an acknowledgement of the ambiguity of tone in the written word and of the tendency of people to always take away the most offensive interpret

I think it's just an acknowledgement of the ambiguity of tone in the written word and of the tendency of people to always take away the most offensive interpretation of the comment. Some people use it as a preface to cushion their unfiltered invective, but it's in everyone's interest to give people the benefit of the doubt in recognition of the ambiguity in what we say.