When I say "monitoring", I mean I make a particular effort to observe and note changes, because I know that if I see an increase in mucous then I will likely start to see pus and blood at some point as well - and I'll spot them sooner if I'm checking. Symptoms like diarrhea, pain, crippling fatigue, joint pain, weight loss and so on come a little bit later for me. For example, last flare I had noticed the changes in mucous etc and reported it, and my gastro started me on pentasa. That didn't change anything (never does, but I don't get nasty side effects either so I figure it's worth a try), so she gets me in for a colonoscopy. That shows inflammation, then I develop severe diahorrea and a week and a half later I'm in hospital having lost 5kg in that week. In terms of timescales - I see an increase in mucous a month or so before the diahorrea really starts, but my blood results are still coming back OK at that point. The inflammation starts to show in my blood work sometimes a few days to a week before I get really sick.
So for me, knowing and keeping track of my early warning symptoms gives me time to try the low-impact drugs first and organise myself a bit knowing that I might be out of action for a while at a point in the near future. Everyone's disease is different, but if you can identify the patterns that happen during the course of a flare then you're better placed to give your doctors useful information about what's happening inside you, and have some sense in your own mind that you know what to expect. That's the biggest psychological help I've found - feeling like I can identify specific markers that indicate whether I'm actually flaring or just having an off day.
If it helps - yes, gross things might happen even when you're in remission. They might or might not be related to Crohns. You should tell your doctor about them, and you should absolutely especially tell them about changes in symptoms, and if it seems like your doctor doesn't listen well you might need to change doctor. Like I said, I see mucous regularly even though I'm in remission (confirmed by blood tests, colonoscopy and biopsy) - I have a lot of historic damage to my insides and my guts function a bit oddly at the best of times. Even so, I personally would be worried if my doctor told me mucous wasn't a problem, because I'm familiar with the pattern I see when I get sick. I would expect them to do some blood tests if I reported seeing large amounts of mucous, and I'd expect they might suggest a colonoscopy if it persisted or was joined by other symptoms. Unfortunately the only way to get familiar with your patterns is to live through them.
Edited a couple of times because I think I was missing the point - I'm sorry if I'm off topic a bit.
