For travelling specifically:
• The Magic Keyboard acts as its own case for the iPad Pro. I wouldn't keep a bare laptop in my bag, but I would throw the iPad-Pro-in-keyboard-case in there.
• The iPad (any iPad) is better for reading books, watching movies, and all the other stuff you do more of on planes/trains/automobiles, than a laptop is. The Keyboard Case holds the iPad up in the air by about two inches (getting the screen closer to your eyeline without straining your neck), and then lets you further position the screen at strange angles (e.g. "inward") for better viewing — angles you can't really adjust a laptop to. And if you want to read a PDF, a graphic novel, or anything else designed to be viewed vertically, you can, at full size — just pick it up and turn it. (Maybe pull the case off to make it lighter, if you're going to be reading for hours.) Basically, the same logic behind bringing a purpose-designed e-reader device.
• If you have a Pencil to go with it, it can also be a reusable piece of paper with infinite "template" content pre-loaded — since you can arbitrarily mark up any PDF or image in the Files app, you can just load on a PDF of coloring-book pages, and now it's a coloring book; or grab a PDF of crossword puzzles, and now it's a crossword puzzle. No purpose-made apps required for either. (If you draw as a hobby, it can be your sketchbook, too; sadly, I'm no artist.) In other words, bringing an iPad also replaces packing those dimestore "activity books", and/or a notebook + actual pencil.
• iPads (or really any convertable / 2-in-1, where you can fold away the angled keyboard part of the computer) are great for showing people the stuff you do / giving people demos — which is something you might be doing a lot at conferences, if that's why you travel. This is a pretty unique use-case; tablets themselves are really "the thing" for this. They maybe replaced... handing out brochures? Having a glossy explainer book printed, and then packing that? Bringing a portable projector + slides?
• Kind of like the recent revival of "intentional dumbphones" that encourage "unplugging", the iPad is designed in a way that still allows for productive work, but makes it less fluid. I can SSH into prod from an iPad, but I don't want to do it for a minute longer than I have to. If you're travelling on vacation, this could keep you focused on relaxing, in a way you might not be if you have a laptop along, tempting you to spend eight hours ignoring your wife and kids to squeeze out that new feature that popped into your head.
Notice that none of those are benefits of the iPad Pro specifically. I don't think that, for at least my use case, there's really much I'd get from an "iPad Pro with Keyboard Case" over an "iPad Air with Keyboard Case." Mind you, I have an iPad Pro... but I bought it because I had the money, and wanted the beautiful color-calibrated display; not because the Air wouldn't have suited my use-case just fine. (Though, when I bought it — 2019 — they weren't yet selling the Keyboard Case for the Air.)