I can understand it feeling uncomfortable or restricting if you're just not used to it (and even I have some tricks I use that don't work without at least one extra layer) but I've heard things along the lines of it being, like, grueling, and I've always wondered why. ^^;
The most recent and confusing example was something I saw on Tumblr the other day, where the artist was like "I challenged myself to do this all on one layer and it took 6 hours; never again"
And the art was just...simple. ._. Like, just a cute cartoon doodle, without any complex shading or rendering, and maybe 20 lines total in the whole image.
And I'm like...I'm pretty sure I could make a reasonable facsimile of that drawing on one layer, in one hour, with my pen-mouse. 30 minutes if I were allowed to do the line-art in pencil first.
So...there must be something I'm not understanding here. ^^; I'd just like to know what it is...