I'll be honest, I only just started using BOTH sides of a page as of last year.
I hope I wasn't the only one scared of "ruining" my pages by doing that. I went through 10 sketchbooks before finally changing it up and doubling the use of a single book.
I'm also one of those people who wouldn't think of tearing out a page in the hardbound sketchbooks I use. I saw some other dude who does that (with a similar type of sketchbook), and I have to admit I found it kind of shocking that he apparently went through it with a box cutter, which is the cleanest way to do it for these kinds.
Those spiral types are nothing, though. It's not hard to just tear a page out and discard it. But only recently would I think of drawing on the back of a page.