I'm not sure at all about this. Have you read this in Harvard's webpage?
Transcript Upload Page 1
The Graduate School requires that one official university/college transcript from each university/college attended--bearing the seal of the institution and signature of the registrar or appropriate official--must be submitted in support of your application. In addition, the Graduate School strongly encourages you to upload a copy of your transcript with your online application.
It looks like it is mandatory to send an official copy, and then it is optional to upload a copy. And the same about MIT. However, this is not the case with Caltech. I ask them through email and the replied saying that you need not post a copy of the transcript, with the online one is enough. What do you think?