I've been struggling with a huge flare and a partial blockage that keeps popping up at the oddest times. We're not sure if it's biological or mechanical, and of course it's beyond the reach of a scope going in each direction!
I had a scope about a year ago and am going back in in a couple weeks. I've had relatively few colonoscopies over the years as SBFTs usually show more than enough of what's going on in there for me.
My mother, she also has Crohn's, has a colonoscopy and endoscopy every year and calls me with all the gory results. I do have to say that having a mom with Crohn's has made it much easier to talk about all this crap. There's no bodily function that we cannot discuss over a meal that will bother us. I do have to say my father has heard way too much over the years!
But I'd have to say that if things aren't bad or bothering you, at least every couple years is advisable. I know the cleaning sucks and that scope tears up our inhumaniods, but it's still better to know what's going on in there.
For me the issue is the cleaning out. Doctors want it done a certain way, normally with Polyethylene glycol, but I'm terribly allergic to it - red hives, troubles breathing, swelling, etc. Luckily my GI tells me to clean out in a way that works for me. As long as I'm clean, he's happy. I actually had a GI break up with me because I refused to clean out with Polyethylene glycol for a scope. I'm better off without him.