With its ability to flatten wide stock quickly and effortlessly, one of the things that my planer sled design has enabled is a little more flexibility and ease when I need to glue up something wide. Ironically (or perhaps not so much), the jack plane often comes into play here. A quick treatment with everyone’s favorite “rough ‘n ready” sometimes saves even more time.
By way of example, I’m working with a bunch of suboptimal cedar at the moment. I need 10-inch (~255mm) stock, and I don’t have any. So I glued up sections of three (crummy) 4-inch stock, first roughing out the stock on the bandsaw, then planing slightly “sprung” edges using a jointer plane. I didn’t make the edges perfectly square to the sides because the sides were rough and uneven from the bandsaw (and the thicknessses varied anyway)–all I cared about was getting edges that would join together.
When doing something like that, you end up with a glued-up board resembling something from the Cubist style, for which the conformist cries out to flatten. And we oblige. For the planer sled to work correctly, you want the face you put on the bottom to be “roughly” convex, but there’s no particularly exacting standard. So you can grab a jack plane to (effortlessly) knock off a bit from the sides near the edges:

Now, you can flip it over, pull out the planer sled, and fix the whole mess in place:

And just like that, you’re ready to feed the whole mess into the thickness planer and flatten it in one shot. The process of knocking off the edges, fixing in the planer sled, and flattening with the thickness planer only takes a few minutes (I spent a lot more time taking the photos and writing up this post).
Perhaps there’s a need for a “moral of the story” trope-ish thing in here, so here you go: The jack plane is invaluable. Even though I don’t need to use it nearly as much as I did in my prep-stock-by-hand days, I’d still be lost without it.