It depends how frequently you want to utilize the HTML content.
If you see the chances of re-using the same HTML content multiple times are higher (e.g. Header, Footer, Social Medial Links or Specific content blocks in the email deliveries) than in such cases you can always create the Fragments in ACS by using email Designers. These fragments are kind of reusable blocks which you can use again and again as needed inside the email templates and you can create email specific local copy as well.
However in case of one time single use you can always use copy the HTML code option of the email delivery as mentioned in above reply.
So all in all it depends in the usage Hope this helps.