I like the Mail Merge and "insert templates" fields.

The collaborative organization! Streak pipelines are the best thing that has ever happened to my sales team. By establishing the Streak pipeline for (in my case) each a sales and on-boarding process, your entire team becomes intuitively aware of (i) the flow of the sales/on-boarding process, and (ii) where the biggest hurdles are in the pipeline that slow down the sales/on-boarding process. My whole team can also add emails to each account, "box" in Streak terms. This is great for when I want to know about an account someone else is corresponding with - I can go into that account's "box" and see all the emails, customizable note fields, and any reminders that my teammate has made. Streak notes also appear beside any message you send or open (if you've already associated the message with a "box"). This is fabulous, because when you're reading or composing a message, you can glance to you or your teammates' notes on the side and have any context you may need.