It depends on how big and complicated you're planning on making your layouts.
With small/simple layouts you can mostly wing it as you go, but if you're planing on big layouts with multi paths and whatnot it'll be faster to sketch it down on paper first, at least the main routes of platforms.
Work with tile based platforms and scenery 32px/64px, then use a math paper as your grid and sketch on it.
You won't have to test everything since you know exactly how high and how wide you can jump.
The tilemap plugin is amazing but it is still not perfect, you can't fill/draw a grid with rotated tiles and you can't select and delete a bunch of tiles and you can't move tiles around, so making changes to your path on the layout can be a little tedious a times.