Here's a little scenario that plays itself out frequently.
I log in to Duolingo in the evening after work, ready to do a lesson. I open the "Practice weakest words" and immediately get the first one almost right. So I get frustrated and quit.
This repeats most nights and I feel like I'm not practicing as much as I should.
But! If there was a warm-up mode, a mode where words and phrases Duolingo knows I know were presented to get me "in the mood", even if it were worth only 1 coin instead of 10, I might stick around to try and get my 100 for the day.
Know what I mean?
I regularly go back and go through all the lessons and repeat each one until I get them all perfectly. It is very helpful if frustrating because of the number of mistakes I make on words that I know very well but translate incorrectly such as the and a simply because of inattention. Of course that is what accurate translation is all about.