My former Galaxy S3 & S5 allowed me to "Add slide" in it's stock messaging app. There are many times where I wanted to send multiple messages to one recipient but by the time I'm typing my 3rd message they've already responded to my first text which then throws off the entire conversation. The "add slide" feature allowed me to write the first message, then I would hit add slide which would basically create a page break in the text box where I could then type the 2nd message, and so on. Once I finished my 3 message let's say, I would then hit send and the app would start sending my texts in order one right after the next. Now the recipient would be able to read all of them before responding.

If I were to do it the way Textra & all other messaging apps work, I would have to type a message then send it, then type a 2nd message then send it, etc. So I'd have to speed type it all the texts hoping that my recipient wouldn't respond to me in the middle of it.

This is a feature I believe many users will find extremely useful once they try it. This could be accessed once we hit the "+" where we access all the icons to add a gif, etc.