I'm coming over from Microsoft and their lines of products. A feature I consistently found helpful were the option to have various unique signatures. I utilized these signatures as canned responses, quick replies, and various other pre-set/pre-designed emails.
It increased speed and productivity quite a bit, especially when you are replying to customers about a few similar things repeatedly. This was something I learned from a few major Real Estate Companies for them to save time and become more productive.
If this is a feature that already exists somewhere within the platform, I'd appreciate directions on accessing it, but I've yet to see it and it would be utilized immediately.