In email templates to know if order only consisted in downloads
{% assign nothing_but_downloads = true %}
{% for line in line_items %}
{% if nothing_but_downloads == true and line.variant.requires_shipping == true %}
{% assign nothing_but_downloads = false %}
{% endif %}
{% endfor %}
{% if nothing_but_downloads %}
SPECIAL CONTENT
{% else %}
USUAL CONTENT
{% endif %}