I Have printed like 5-6 models at time, different scale, different difficulty. Like Butelczynski said, i like doing simpler models for a break from doing the harder ones. Also sometimes simple models are just beautiful! Currently i have the big boss model wich is the howl's Moving Castle which i go and print 10 pages and cut them/edge-color them when i feel like it, no rush at all. Beside that im working on not-as-big models such as Glados or Deoxys or some other 4-10 page model. and for breaks i go for anything else simple/funny/weird model i find online like Awesomo, some popfolds (cube-ish figures) and other 1-3 page simple models just for fun. Also as a break i started doing many mini figures for RPG, from here:
Fantasy Paper Miniature Models
Apart from hoping that someday they will be used on some d&d campaign, they look pretty neat:
https://imgur.com/a/KvDgsdn
Although im taking a break from making them because some of them arent that well-made (mostly spherical ones), at least for my taste and also its very hard to cut the outline details on such small size (and also edge-color them), on hard paper. I think the art should be somewhat simpler or different so it helps with the cutting (talking about 2.5 figures like skeletons etc). Also some black outline would help, which i didnt do in photoshop and i had to do with a marker. Next time ill outline them in photoshop first.
Until now i have never thrown a model away. Glados was about to have a bad time, but i fixed it and its fine now, lookign great hanging from my shelf :D Although it being my hardest model done, i cant really talk about mistakes and having to throw a model away so there's that :P