When you right click on a tab and hit “duplicate”, it essentially creates a mirror of the original tab. Changes are reflected in both.
When I first used Aseprite I assumed that it was a way of duplicating the project. Sometimes if I want to do something drastic, such as merge all the frames and then copy a frame, I don’t want to do this in the original file, and “duplicate tab” would work very well for this.
There are two duplicates:
Maybe we could change the View > Duplicate View label to avoid confusion in the future (?) 
Hmm…it’s tough because even though it sort of makes sense where it is now, I never thought to try sprite > duplicate and see what it does. I assumed “duplicate” was duplicating something else since canvas options are often under “image” or “edit” in other software. I tried right clicking the tab before knowing if duplicating the project was even possible, assuming that’s where it would be.
Maybe duplicate (the sprite) could be called “duplicate sprite”, “duplicate file”, or maybe “duplicate project”, or under the under the file tab?
I also think it would be best if you could duplicate the project via right clicking the tab. Also this is subjective, but personally I’d prefer if it did not have options, since usually my goal is speed in accomplishing a temporary task.
For those who want to save it as an iteration, the filename could be automatically set to “project name_#+1”, with the path being the same as the original file, so that save can be used right away without the need to use save as, which opens the explorer. (Since if they want to do this, they could do it on their own)