Worth it: mobile-first
80%+ of opens are mobile. Single-column, large tap targets, readable at glance. Design starts mobile.
Worth it: dark-mode compatibility
Black text on white backgrounds breaks in Gmail dark mode. Use PNG logos with transparent backgrounds. Test in both modes.
Not worth it: advanced interactivity
AMP email, interactive carousels, accordions. Inconsistent support, maintenance nightmare. Simple hierarchical email wins.