Interesting that this topic came up, as I have recently begun building the Medieval Fortress, (book), and although I began in Survival, I realized quickly that with my limited play time, it would probably take me many years to complete that way. A few years ago, I had tried to switch a world to Creative, and either it was me or the world, but something glitched, and I have been forever afraid to make that switch, until I began the Fortress. I decided to give it a try in Creative, and love it. I plan to switch back to Survival once the main Fortress is built, and play Survival from there, as if I landed in this place that was already there!
I also decided to try going into the Nether in Creative. I hate the nether, am deathly afraid of getting burned by lava when breaking blocks, so decided to try switching, and found I loved that too! Went back and forth, when I found an ore I wanted I would switch to Survival, and back to Creative to make my tunnel.
The thing is, I play this game to relax, at night after working all day, (I am an older female adult) and if this makes it more fun for me, then so be it! Like someone else said, it's only cheating if you feel like it is, and I hope to eventually get to the end, and maybe this technique will help me stick in a world long enough to do that.