So, let's say you want really beautiful emails sent from Salesforce. You build all the HTML to make them look amazing and add a bit of Visualforce to make them more dynamic. But then you add a couple of more templates that all share the underlying design and the only thing that is different between them is the dynamic text in between the header and the footer. This means the design is now hardcoded into every single email template and if the design template changes you have to change them all.
So my first instinct is to use
apex:composition in the email templates but I'm pretty sure that I read somewhere once that this is not supported. If this is the case - what is the alternative? And are they any plans to fix this? Is there a way to do this in Lightning email templates?