I've been reading this thread for a while, and have a question. Let's say you are skiing down an old lift line. It's narrow and goes straight down the mountain; the pitch switches from steep to not-so-steep and back again, big big rocks are present under the snow in places, or visible through sheer ice, and those rocks influence the shape of the bumps; and this lift line has got double fall lines here and there. There is no rhythmic line anywhere through the days-old bumps, and the sudden drop-offs on some massive 6' tall bumps are 90 degrees on the back side. Getting across those troughs is impossible for mere mortals. Even along the outside edges of the trail, next to the trees, the bumps are big and the troughs are deep.
I'm no expert, but I love limping my way down these trails. Skiing the troughs is really my only option in some parts, given my current skill level. However, there are ski gods who blaze past me skiing more or less straight down the side of the trail. They sliver around the sides of those massive elephant-sized bumps that I have to stop on to plan my route around. They are not skiing the troughs; they are doing what this thread is suggesting. I'd like to be able to do that too one day, or at least come close to it (dreaming!).
So here are my questions: In the case I just described, skiing through the troughs is the slow-and-careful non-expert way down. Skiing down the edge next to the trees, crossing the troughs, is the expert way down. Is the situation I just described different from the bump runs most posters on this thread are talking about? Most everyone on this thread is promoting staying out of the troughs, even when the moguls are big. Is that because they consider skiing through the troughs too difficult for their readers/students, or do they find skiing the troughs undesirable because it's what slow people with low skills do?
I wouldn't go so far as to say "this is the beginner line, that's the expert line", at least in terms of the skills required. But when the troughs get big, it seems to be most peoples' instinct to ski down through them, the same way we would walk on a paved path across a grassy field or the way we keep our car between the lines on the road. The problem with this line is that it can often dictate the path we take down the slope and it can be very hard to get out of, especially when the troughs are big and icy.
For most beginner bumpers, I would expect that a line like this gets skied at pretty slow speed, where an experienced skier might be able to rip it up just as easily as any other line on the mountain. But all things being equal, its probably going to be more fun and easier on your joints to stay on top of the bumps as much as possible when you're dealing with conditions like you describe. As icy as things might be in the troughs, if there's any decent snow to be found its almost definitely going to be on top of the bumps. I think the main obstacle is to make your brain see a line that doesn't simply follow the path of the troughs.
My preferred way to train this type of skiing is to ski an easy-ish bump run while making a constant, short radius turn (say, 1 cat track wide) regardless of the shape/pattern/size of the moguls in front of me. The result will be that you're going to end up getting a feel for striking moguls of various sizes from various angles and making turns both in the trough and on the bump itself. When I'm skiing moguls "for real" on something more difficult, I can draw on that experience.
At the end of the day though, and its been said before, there's no single "correct" line. Everyone will see something different in the bumps, whether its a perfect zipperline, a nice rounded trough that you can ski through like a banked corner on a race track, or a pair of bumps that would be a good spot for takeoff and landing while airing over an icy trough. The ski school director at my hill last year would always talk about being "exciting" in the bumps. Didn't matter if you fall, the key was to try new things and keep figuring out different ways of navigating through the rough terrain.
Sorry, got on a bit of a ramble there, hope that at least partially answered your question.