100% Pro mix it all up. Short, long or in-between, if it is interesting then it is interesting. People like variety, we have made for the big screen almost 2 hour long movies, (someone figured out that 2 hours was about the max time someone could sit on their ass in a theater seat). the 1 and half hour TV movies, the 30 minute sit-coms, and then some really long movies such as Tenth Kingdom and a few others. Oh and lets not forget about the on-running Series, and the option now-a-days to sit and binge watch them all.
Books/reading material are pretty much the same you have short, medium and long forms of them also, so a nice mix and variety of choice.
I agree and it is going to depend on the current mood as well as the needs of the audience at the time. I don't think there are many people who scroll memes all day.