Mention painting wet into wet with watercolour, and many a person seems to have a vision of a wildly spreading chaos like this: (video link)
Whereas wet-into-wet can be a tightly controlled technique. It all depends on how you wet the paper and how you apply the paint.
If you’re on totally dry paper, carefully wet a specific shape, and then apply paint within this area only, it won’t spread out into the dry paper. As I’m doing here with a shape that’s excessively wet to illustrate the point: (video link)
(My apologies, do not adjust your glasses, the focus does get a little fuzzy at one point in the video.)
It also shows how a good flat brush gives you a very sharp edge or line and control. Note too how I’m using my little finger to steady my hand on occasion; it’s not something I consciously do, though I know I do it only if I’m painting sitting down.